Invasive Species

6

The Brighton & Hove Connection underground system had been erected over the course of five years some thirty decades ago. It was built entirely with maglev technology, so all of the trains were magnetic, 'floating' trains, though it had been a source of much controversy for a long time. Mainly because Brighton was not a major city, nor a particularly populated city, nor a centre for any kind of industry outside of environmental activism, Gay Pride, and tourism. So the decision to build an underground system there, of all places, didn't wash well with the country's actual major cities. Birmingham still didn't have a subway, Leeds had one under construction, while Manchester had been granted the second after London. Glasgow had one, while Edinburgh remained geographically complex, and Cardiff seemed relatively ambivalent to the whole thing. Despite this, the BHC system only had three lines; its most ambitious one went directly into London; its least ambitious one went directly to Hove; its middle-ground circled Brighton's few, small boroughs; and it only had one large, central station (Buckingham Central Station) where all three lines convened – though 'large' was being generous. The Doctor supposed it had a WH Smiths and a Starbucks, and that qualified it as a 'major station.'

It was true that they did not frequent the tubes. They could use the psychic paper as a nifty, fake permit to park anywhere in the city, but there were also still plenty of buses and Brighton wasn't so large they couldn't walk into town. The one time they'd used it, it had only been to go to London for the day a while back, but it wasn't much easier than taking a regular, above-ground train (frankly, she thought the Brighton-to-London line was unnecessary, though the tickets were cheaper.) But no matter how little time they spend on the underground, it was obvious that it was not supposed to look like how it did that day: completely overrun with roots.

Roots the thickness of barrels snaked their way across the walls, the ceilings, up the stairs, drooped down from above and created walking hazards. Where once there had been obnoxious, LED screen advertisements pointing at commuters from every direction – advertising vegan health drinks, ocean cleaning endeavours, new movies, and electric cars – there were now just trees. The roots had crawled across every available surface and out of the mouth of the station entrance, burrowing through the asphalt on the roads and growing into the bizarre trees like the one in the middle of their driveway. It was only a matter of time – perhaps hours – before the trees started plundering houses directly, breaking through the foundations to emerge from the depths and drag people below from their own living rooms and kitchens. All of this was illuminated once the Doctor found her torch buried at the bottom of her transdimensional bag. Clara used her phone for light, and if that failed the Doctor knew she would resort to one of the dim cigarette lighters they had.

"Okay, then," said Clara quietly, "I guess you're right. This is the place."

"Did you doubt me?" Clara shrugged. "Typical."

"What's typical is you denying me of sex and then taking me dungeon crawling."

"It's not a dungeon," the Doctor dismissed her, "Just train tunnels." The daylight dissipated behind them as they descended down the steps of the Fiveways Station, situated just across the road from the Travellers Rest. It was as though the roots around them were breathing, the station swelled with them, and the Doctor sometimes thought she glimpsed them move or heard sinister rustling. "What did we do with the lantern?"

"What lantern?" Clara asked, lurking at her shoulder, keeping her voice to a whisper like the roots were listening in.

"Didn't we have an old storm lantern? I thought… we got one from…" She paused to think and Clara observed her in the electric torch-light; it made Thirteen's face look washed out and strangely grey. Clara waited for the Doctor to remember, until she actually remembered herself what Thirteen was talking about.

"Oh – it's in the van. We took it with us when we drove to St. Ives for the weekend, in June, because you said it was 'atmospheric.' And then there was a storm the whole time, so it came in useful." Unfortunately, the refurbished VW camper didn't have a toilet; it was its only real shortcoming. That and the fact that even they had to duck while inside. "You remember? Because you wanted to go surfing and I wouldn't let you."

"Yeah – why wouldn't you let me go surfing?"

"Have you forgotten that whole thing where you jumped into the sea and drowned, or-?" Clara asked sarcastically. Of course the Doctor had not forgotten that, though she sometimes did (among other, much more sensitive things.) "Not to mention that you don't even know how to surf."

"You can never learn if you don't try."

"Yeah, I don't think in the middle of a storm is the best way to learn."

"It's when the waves are highest!"

"When they're deadliest, you mean."

"Potato, po-tah-to."

"This is exactly why I don't let you in the sea," said Clara. The Doctor was very close to arguing with her about the entire idea of Clara having to 'let' her do anything at all, but resolved not to. After all, the list of things Clara would and would not 'let' her do was very short, and consisted of 1), go swimming in open water in a non-emergency, and 2), have freedom over her own money. There was also a list of things the Doctor would not let Clara do, however, which were 1), use any and all kitchen appliances and 2), borrow any of her tights, because Clara had an unpleasant talent for laddering them. "Do you want to go back and get the lantern?"

"No, it's fine. So long as I know where it is," she said. "We should go back so St. Ives, when the weather is nice."

"Why? There's not a lot there. We live on the south coast already," said Clara, "We should take the Eurostar and go to Paris. The Eurostar's magnetic now, right?" It was.

"What do you want to do in Paris? We've been a lot."

"I know, I just like it. It's more interesting than London. We could take Mattie."

"Is this a romantic getaway or a family trip?"

"I don't know…"

"If it's a family trip, we'd have to take Rose. And Rose hates France."

"So let's go to some other capital – let's go to Edinburgh. We could go see the Vaults, we didn't get to last time we were there. Rose will go to Edinburgh, she loves Scotland. And there's all the Scottish people. With their accents."

"Ha, ha."

"Why don't you have a Scottish accent?"

"I do – in the other universe, remember? Old, Scottish man."

"Oh, yeah."

"Incapable of loving you."

"Right."

"Sort-of, inadvertently caused your death."

"Mm. But I did get to marry a pretty fit girl because of all that." The Doctor stopped in her tracks just to glare at Clara, who only smirked. "When is Jenny coming over for dinner next? Shall we invite her to Edinburgh with us?" The Doctor shook her head and didn't answer; Jenny was coming for dinner next week, which Clara knew full-well because she had a made-up schedule for them in her head she kept track of religiously. "Assuming we don't get eaten alive by vampire trees."

"What about Cohen? Maybe she'll want to go back to Edinburgh."

"She's Glaswegian."

"Are you sure?"

"Quite sure. So, where are we going? Now we're down here." Admittedly, the Doctor's plan hadn't extended that far. She'd just about scraped together aerosols and lighters to use as a last-ditch attempt at self-defence and thought the next stage would just present itself to her once they were in the dark train tunnels.

"Uh… we should go left. Towards Buckingham."

"If you say so," said Clara, aware that the Doctor was just guessing at which way they should walk. But it didn't really matter, the line went around in a circle anyway. Technically, left or right would get them to Buckingham Central, it just so happened that left was quicker. It was only three stops away. "Come on, then," said Clara, dropping down from the edge of the platform onto the root-covered tracks. She took the Doctor's torch while she followed, landing awkwardly on the uneven surface. "What, exactly, are we in here looking for?"

"Missing people?" the Doctor suggested.

"You don't think they're dead?"

"Maybe not yet. Takes a while to drain a whole human of blood, depending on the method; I doubt the trees are cutting anybody's throat, so they must be doing it another way."

"Another way, like…?"

"I don't know, proboscises? Unless it's not just the blood, and they're eating them? But a Venus flytrap can take up to twelve days to fully digest its prey. If it takes these things twelve days to do whatever it is they're doing to a human, then we're not even halfway through the process – there might be a lot of people we can still save. Maybe even all of them." She wasn't sure whether she believed that or not. "But I guess Audrey II was a big, alien plant and it always ate people very quickly."

"It also sang doo-wop songs, so, I'm not sure how comparable it is to this situation."

"We don't know that these trees don't sing doo-wop songs."

"Amy and Donna met that one who sang pirate shanties and killed Amelia Earhart. Or so they say," Clara continued sceptically, "Personally, I've never been convinced that that entire story wasn't just a fever dream. You know, there's a lot of stories about man-eating trees in folklore – there's one about a blood-sucking tree from Nicaragua, the vampire vine. Its vines were supposedly covered in tiny suckers, like tentacles, and it ripped the flesh from anything that touched it. Probably more interesting is that the whole story is a load of shit, though – some guy, a newspaper editor, made the whole thing up and published it pretending it was true in the 1880s. The story was published before Dracula, though. But after this big, New York hoax about a man-eating plant in Madagascar, which was in the 70s."

"Same time as the birth of western vampire fiction."

"Oh, of course," said Clara, "But the entire Victorian period is obsessed with the macabre. Frankly, the obsession hasn't gone away, it's just atrophied into true crime… H.G. Wells wrote that story about the blood-sucking orchid. I was thinking about getting a yucca, you know."

"Were you?"

"I was. After this tree invasion, I'm not so sure… and I meant, maybe it's to do with developments in science; understanding the role that blood plays in the human body, which led to a boom in fiction about parasitic monsters stealing blood. Maybe I should do another degree – medical history? Cohen's a pathologist, do you think she knows anything?"

"Maybe, but she still doesn't like you."

"But she might like talking to me about man-eating plants."

"If you want to do another degree, then go for it," said the Doctor. "While you've been talking about plants, however, I've been thinking about fungus."

"Are fungi not plants?"

"No, they're fungi."

"So not plants?"

"Is a spider an insect?"

"I… yes…?"

"It's an arachnid, it's different. Anyway, have you heard of mycelium? It's an underground fungal network, a mushroom internet. The fungi connect all the other living creatures together, too, so that they can share resources, like food and water."

"And memes," said Clara. "You know, if it's like the internet."

"Everything you say makes me hate you even more."

"Thanks."

"My point is that I think all the trees are connected to each other – they're not separate plants. If anything, the roots in these tunnels prove that theory."

"So the roots just, what, lead to the other trees?"

"I don't think so… it reminds me of the Lankin, have I told you about the Lankin?" Clara stayed silent, indicating that the Doctor had not. "It's an alien shapeshifter made out of vines, partially telepathic, sniffs out grief. It finds people who are grieving and then comes to them at night in the form of their deceased loved ones, working telepathically to find out all the right things to say, and then convinces them to come with it to 'heaven,' when in reality it's eating them. A million vines and stolen faces extend across a whole city, appearing overnight, and eventually take over the whole planet that way, stealing an entire species for themselves. But they were part of one creature, all the vines led back to one central entity."

"And how do you kill a Lankin?"

"Poison it, with negative emotions, like anger. You remember the Coal Hill kids?"

"I do not."

"Well, they fought a Lankin."

"Great."

"I think these trees might be similar, they might have a locus," the Doctor explained, "One big, like, plant-heart. I mean, technically I don't think these things even count as plants, if they devour flesh. Like, sure, a Venus flytrap or a pitcher plant also eats flesh, but they dissolve it in enzymes. They do photosynthesise. Although – and here's the science bit – even on Earth, you do have heterotrophic plants."

"Heterotrophic?"

"Parasitic, they get their nutrients by attaching to other trees and plants and stealing from them. Beechdrops, or broomrape."

"Sorry, did you say broomrape?"

"Yeah."

"Like… 'broom', and then 'rape'?"

"I said it's a parasite. Even mistletoe steals nutrients, though it's not truly parasitic, because it still contains chlorophyll. Broomrape doesn't have any chlorophyll, and that's why if you see one, it's not green. They're sort of… coral. Salmon. There's a Native American tribe who use the clustered broomrape to cure haemorrhoids. You put the plant up your, uh… y'know. Where you get haemorrhoids. The Zuni do that. Maybe it works? I couldn't tell you. Did you see the leaves on those trees up there? They're red and orange, not green."

"It is September, the leaves are starting to turn."

"No, they're heterotrophic organisms. As in, non-photoautotrophs. They don't photosynthesise because they don't get nutrients from the sunlight, they steal them, from the humans they're eating. The only positive about all this is that the dumb things will probably digest things just as slowly as Earthling plants do."

"Okay, so we have to run a stake through the heart of the vampire-tree-internet?"

"I wouldn't put it that way. And we also don't have a stake. We have aerosols."

"Well, the stake is proverbial."

"Of course it is. I wonder who the Lankin would show me if they had to… I've got a lot of grief, I'm sure they'd come for me. But I don't think they'd be reasonably able to appear as an entire species. And besides, seeing the all the Time Lords back again would probably stamp out a lot of the grief I have for them all being dead," she mused. "Maybe it wouldn't be able to get a read, to figure me out."

"How do you know they'd even want to eat a Gallifreyan like you? And maybe you're too old. Rancid."

"You sure know how to compliment a woman. To be honest, there's only one voice they'd ever have a hope of tricking me with – but you're not dead. So maybe I'd be immune."

"Really?" asked Clara, "You'd go to evil alien fake-heaven for me?"

"When you put it that way, how could I ever refuse?"

They reached another station, Hollingdean Station. After that it was Hanover, and then Buckingham Central. Their progress was slow but sure, and they'd get to Buckingham soon enough. The roots were only growing in intensity, however. They had infested the underground lines in a matter of hours; the tube had certainly been open yesterday, late into the evening. They couldn't even see the maglev tracks beneath their feet, they were walking across the thick, snaking tree roots, which she could have sworn she sometimes felt moving, like they were intrepid explorers stupidly wandering into a python's lair.

"Are you okay with having Steph in the house?" the Doctor asked eventually, "She is a little… obsessed with you. What if she does something? Steals a photo, or goes through our underwear drawer?"

"If she steals a photo Mattie will notice, and our bedroom door has a biometric lock just like the study. And I don't think she would steal our underwear."

"How do you know? She might have a thing for women's underwear. You know, like you do." Clara glared at her in the gloom. "What? It's true. Any and all typically-feminine undergarments-"

"Yes, alright."

"Just one mention of the word 'garter' and you're-"

"Shh."

"I'm just-"

"No, shush," Clara stopped dead in her tracks. Obviously, there was something more important going on than the Doctor trying to annoy Clara about her 'tastes' on purpose. When they paused to listen, they both heard a noise; a distant, slithering, grating, drifting from just outside of the range of their lights.

They had less than a second to react when a tendril shot out of the shadows, fast as a bullet, at head-height. If Clara wasn't so used to dragging the Doctor out of harm's way, that could have been the end of her – she could have had her brains smashed to pieces by a lump of wood travelling over a thousand miles an hour. Clara grabbed Thirteen and pushed her back towards one of the walls. The root moved like a tentacle, stopping and beginning to retract itself, slowly, like it was searching for them.

Clara did not remove her arms from around her as they watched, in silence. Something else began wrapping around their legs though, as they pressed themselves against the wall. It was only unfortunate for them that the wall was covered in just as much foliage as everything else.

"Shit!" Clara cursed, trying to drag herself away as a multitude of smaller roots tried to bind both of them so they couldn't dodge the big, tentacle-y root. Lucky for them Clara could turn intangible. But freed from the wall, they remained vulnerable to the massive, monster root. The walls began to writhe around, moving to make way for more killer plants to get at them. The Doctor dropped the bag to the floor and hastily unzipped it. "Hurry up, hurry up," Clara implored.

"I am!"

They weren't quick enough to avoid the big root's second attack, though, as it lashed again, this time at Clara. She forced it away with a telekinetic blast strong enough to send it smashing into the tunnel wall. The strength of Clara's telekinesis was enough to rival the strength Rose wielded with her bare hands, allowing her to snap the sharp end of the root clean off. It writhed like a beheaded snake, but its progress didn't halt at all. It bled from the stump and tried to strike her again, which she was able to duck, drawing the attention away from the Doctor as she fumbled with the lighters.

"Seriously, I don't really know how I'm supposed to fight a tree!" she protested, ducking again. She couldn't do anything except keep pushing it away, but within moments a second root plunged towards them out of the train tunnel. Some of the roots underfoot also began moving, trying to trick her, make her stumble. It worked; Clara was briefly disoriented as she rolled her ankle, falling into the wall, and a root tore at the back of her leg. The Doctor didn't see exactly what happened, dimly aware that Clara had suffered an injury and collapsed.

She finally retrieved both a working lighter and a can of deodorant that wasn't completely empty, able to come to Clara's aid right as one of the roots reared itself to strike a killing blow. She stepped in front of Clara and blasted a stream of flame at the tree, the largest root catching on fire instantly. It flailed uselessly, smacking itself against the walls in an effort to extinguish the blaze. When the second root tried to swipe Thirteen, she gave it the same treatment. The makeshift flamethrower was enough to ward off their attackers, the two assailants charred as they retreated, retracting themselves into the shadows.

"Are you okay, Coo!? What did it do?" the Doctor dropped to her knees next to Clara to get a look at Clara's leg. There was a gash across the back of her shin, and while it was bleeding, the tree had managed to miss any major arteries. The wound was jagged and grisly though, leaving the Doctor more concerned about any risk of infection. "Alright, you're gonna be fine, the bleeding's not that bad," she talked as she began to rummage in the bag again for the first aid kit it possessed.

"Now we're definitely not getting a yucca," Clara complained, holding her leg and wincing. The Doctor managed to find a roll of bandages.

"Put some pressure on it," she said. Clara did just this, though it clearly caused her a tremendous amount of pain.

"Stupid trees… stupid tube…"

"Yeah, I know. Keep still for me. I don't think it'll take too long to heal, but I'll wrap it for you to be safe. Thanks for protecting me."

"You don't have to thank me."

"I'd hate for you to think I'm completely ungrateful for everything you do for me."

"We should go to the Riviera again," Clara tried to change the subjects as she lifted her hands away so the Doctor could start to wrap the bandages around her shin.

"Why?"

"Because Zelda won't stop calling and inviting us to Monte Carlo."

"Not because you want to stalk Grace?"

"I don't even think Grace was born yet, when Scott and Zelda spent their time down there." Clara was right, she hadn't been born at that point in time. "I don't know why you won't let me meet her. I've still never seen the two of you in the same room together…"

"Ha, ha. You think I'm gonna dump you and go marry into the royal family of Monaco, do you?"

Clara shrugged, "Maybe."

"I do think you're the only person who sees this resemblance."

"Do you know she wore glasses?"

"You're unbelievable."

"I'm just saying… I wish you would wear glasses more often."

"Of course you do." The Doctor only half paid attention while she wrapped the bandages around and around, looking up every so often to search the shadows for more violent trees. "Jenny still has those night-vision glasses. They'd be pretty useful right about now. Look in the bag for a safety pin, could you?" Clara did so. "I'm serious about Edinburgh, you know."

"I'll go anywhere with you, you know that. We can go in half-term, if you want?"

"Sure."

"…If you ever want to go somewhere with just us, then I'm fine with it, you know," Clara said, finding a safety pin and handing it to the Doctor. "Like, Mattie's great, but we still had a teenager sprung on us out of nowhere. Not to mention Rose hardly leaves."

"Sounds a bit like you're saying you want us to go somewhere alone together."

"I can't lie and pretend I don't like it when it's just the two of us." The Doctor smiled, fixing the bandages with the safety pin.

"It's just the two of us right now."

"Us and the plants."

"There – how's that?" she asked. Clara tried to put some weight on her leg and flinched.

"It'll have to do." The Doctor picked up the aerosols and lighters and dropped them back into the bag, slinging it over her shoulder again, retrieving the torch from the ground.

"I'll help you, c'mon," she stood up and helped Clara to her feet.

"You don't have any of my sister's old walking sticks in that bag, do you?"

"No, you know how protective she is of those," said the Doctor, wrapping an arm around Clara's waist to keep her upright. Clara held onto her as they continued deeper into the tunnels.

Clara now struggling and the Doctor having to support her as she limped, they went on for quite a while without talking about anything. Listening into the darkness, trying to spy any more violent roots and pre-empt a follow-up attack. Hollingdean Station floated towards them out of the gloom, just as overrun as all the others. She asked Clara if she wanted her to jump up onto the platform and go steal a drink from a vending machine, but Clara said no, so they continued their slog.

"I think those tentacle-roots are how they're taking people. Dragging them down from the surface." Clara made a noise which meant she agreed with this but was focusing too much on trying to walk with her injured leg to form a full sentence. The Doctor continued to think for a while, until trying a different approach to try and distract her from the wound. "Hey, d'you remember when we ran into Missy? In that maze?" Clara frowned in thought. "It was when I went back in time. I kissed you by accident, when I wasn't meant to."

"Oh."

"You were trying to avoid talking to me? Because of our volatile sexual chemistry?"

"Uh-huh."

"You fell in a cave and got a rock impaled in your leg. This reminds me of that. Only less awkward. God."

"What?"

"It's crazy."

"What is?"

"It's crazy how crazy you were about me."

"Still am, against my better judgement."

"Do you wanna know a secret?"

"Do we have secrets?"

"I have the apology letter you wrote me for when you tried to kiss me," she said, "I kept it and brought it back to the future with me." Clara stopped walking and looked at her with an expression even the Doctor couldn't quite decipher.

"You're incorrigible."

"I like how ineloquent it is. You gotta understand, Coo – for a long time I've been married to a celebrated poet. And then there's this letter, this total throwback, and it's… clumsy. And adorable. There's something uncanny about the great C.R.O. Fantoma being unable to string a sentence together."

"Yeah…" said Clara vacantly. She wasn't fully listening, off elsewhere while the Doctor reminisced about what was her recent past but was a long time ago to Clara. She did re-read that letter on occasion, imagining Clara's younger self daydreaming about her and resisting the urge to follow her around. It was funny how Clara was still known to behave so erratically around Sally Sparrow but supposed maybe Clara's swooning was more to do with unattainability than anything else.

"What're you thinking about?"

"Oh, nothing. I'm just – I'm worried. About these trees, and the people they've taken, if they're gonna be alright…"

"You worry too much. Sometimes I think you're all worry and not much else, and never worrying about yourself, either. But then, what's a girl to do? Complain that her wife is too empathetic? God," she began as though she were in conversation with somebody else, "My darn wife was at it again last night – caring about people. Helping them. Listening to their problems. Being kind. I can't stand it. If only I could just wallow in self-deprecation and wanderlust for the rest of my natural life without somebody hanging onto me, being all supportive and concerned for my general wellbeing." Clara laughed. "And did I mention how pretty she is? I can't even look her in the eye! It's like staring into the sun. I'd almost be able to bear it if she wasn't so clever and funny on top of all that. Never fails to make me laugh when I'm upset about something, what's anyone to do with a woman like that? I'm thinking about divorcing her."

"I would," said Clara, limping, "Sounds like a nightmare."

"Well every time I try to divorce her, she sucks me back in with the poetry, the piano music, the charm, the face, and I end up marrying her again! It's obscene. I even forgive her for smoking."

"I'm dying for a smoke right now."

"You're quitting."

"Mm… still not sure what the point is."

"Save money?" the Doctor suggested.

"I suppose."

"You've got too many vices, you've gotta pick the one vice, and stick to it."

"If I remember correctly, you did refuse to indulge me in my favourite vice just this morning. So, unless you mean turn to alcohol, you're going to have to be a bit more cooperative."

"Ha, ha."

"I'm serious – if you just get off with me every time I want a cigarette-"

"We'd lose our jobs, I'm sure."

"Spoilsport." The Doctor smiled, amused, but the conversation dwindled for a while. Clara still flinched every few steps as they ventured deeper and deeper into the underground system. "Trees haven't come back yet."

"They don't need to."

"How do you mean?"

"Think about it – the roots come out to drag people down into their lair."

"And?"

"And, we're heading right into their lair anyway. They don't need to exert any extra energy. And maybe they're scared of my flamethrower."

"'Flamethrower' is being generous."

"I'm a generous person."

"I'm yet to see much evidence to that effect."

"Very funny. How's your leg?"

"…Sore," Clara mumbled after thinking, "Don't let go of me."

"Beginning to think you just want me to touch you."

"How could I not? After you denied me-"

"Shut up. I don't understand you. You've almost had your leg ripped in half and you're still horny? Like, come on. This is what I mean about vices, you have an addictive personality."

"Does that mean I get easily addicted to things, or that people get easily addicted to me?"

"It's the first one, you know it's the first one, you're unbelievable… careful here, the roots are getting bumpier." The number of roots increased every time they passed a station, clearly all leading somewhere, as she had speculated. They were finally approaching Hanover Station, and then there was (she hoped) just Central afterwards. All this walking had taught her was that Brighton was certainly not big enough to justify having a tube system at all, a tube system which was going to be out of commission for the next few weeks while the trees were cleared out. Provided they succeed, that was. "Are you sure you're not bothered about Steph? About her befriending Mattie?"

"Are you sure you're not bothered about Steph?" Clara challenged, having to go very slowly on the crisscrossing, uneven roots. The tracks and most of the walls were now completely obscured once they passed by Hanover Station, as though the tunnel had been dug by the trees and not by the council.

"I'm a little concerned that she might start telling stories."

"Stories?"

"Lies. About you, us, I don't know."

"I'd lose my job," said Clara, "But I don't think Stefani wants me to lose my job. And besides, I teach her English, she's not so good at making things up. Not convincing things, anyway, I'm sure she has an active imagination. As it is, she thinks I'm oblivious to how she gets Jakub to help her with all her homework."

"Wait, shouldn't you do something about that? She won't have Jakub to help her in an exam."

"You're saying I should start tutoring her? Privately?"

"That's not what I'm saying."

"I've seen films with that exact premise."

"'Films'? Is that what you call them?"

"Look, I just… I've heard them say things, the Kaczmareks, about their parents. I know teenagers tend to exaggerate, but Steph told me they're not even worried about Jakub, not even looking for him, after he didn't come home all night. And then didn't care about her going out, either. And you know how she is, sleeping around – she's only fifteen. It concerns me. Even I didn't get that bad until after… well, you know. I just… call me naïve, or optimistic, or tell me I'm worrying too much again, but I think she could benefit from having adults in her life who actually do support her. I don't want her to turn into me, because there's next to no chance that she'd meet somebody like you. And you help me with my… trauma, I guess, more than anything else ever has."

"Yeah… yeah, no, you're right. I guess their parents being terrible is no reason for every other adult in their lives to give up on them and be terrible, too. The last thing you want is either of them doing something reckless because they don't have an appropriate adult. Like joining the mob."

"Well, Jenny does have a particular knack for falling in with organised crime wherever she goes. You remember when we went and saw Queen that time and somebody convinced her to start selling amphetamines after we'd only been there for twenty minutes?"

"How could I forget, my only child, a drug dealer. And at a Queen show, too. My forgiving her is how you know love truly can be unconditional."

"I wouldn't worry about it too much, Ravenwood went mental when she found out."

"Is your leg better yet?"

"…Maybe."

"You don't have to pretend it's still hurting to get me to maintain a level of physical contact, you know."

"Eurgh, maintain a level of physical contact. You sound like a sociologist."

"I just thought it would be a bit too crass to ask if you want me to keep touching you," she said, relinquishing her hold around Clara. Lo and behold, Clara managed to walk again without assistance, limping even less than her sister on a good day. But the Doctor held out her hand, switching the torch to the other one.

"…Thanks," said Clara, taking it, lacing their fingers together like they were on a real date and not on a crusade to kill an alien garden. "Haven't seen anybody else down here. What do you think that means? No more kidnappings?"

"I don't know. Maybe we concern them? Maybe they've got enough for the time being?"

"Enough for what…?"

"I dread to think. Maybe it's just not able to continuously consume."

"For once I'd like to just have a few weeks without alien intervention like this. They could at least wait until the holidays to start invading – I've got marking I should be doing."

"It's the first week back, go easy on them."

"No, I had them write summaries of To Kill a Mockingbird to check if they actually read it over summer."

"Then I hope you enjoy reading thirty poor recreations of its Wikipedia page."

"Mm, but I have a cunning plan," said Clara, "I'll just check everything against Wikipedia and Spark Notes. I can still tell if they've read it. And besides, at least it'll force them to read a synopsis, so they'll learn something if they've copied it out by hand."

"You could try teaching them what happens in the book?" the Doctor suggested. Clara glared at her.

"It's easier if they actually read it."

"Yeah, but, it's just events."

"Them already having read it makes more time for other things."

"Like mock exams."

"No. Like… alright, fine, like mocks, sometimes – but also historical context. Which reminds me, I need your help with a lesson plan about segregation."

"Didn't I help you with that last year?"

"Yeah, but… I lost the notes."

"Did you lose the notes, Clara?" she challenged, "Or is this an excuse to spend time with me?"

"Pfft. I don't need an excuse to spend time with my wife. I suppose I haven't looked particularly hard for the notes, but really, when something's lost, it's lost."

"Like the spark in our marriage."

"Exactly. What would be the point in trying to find that again? It vanished a long time ago. A bit like my notes on To Kill a Mockingbird."

"I can't believe you think coming up with historical notes on Harper Lee is an acceptable pretence for trying to touch me inappropriately."

"What would be an acceptable pretence? Out of interest?" she asked unconvincingly. The Doctor shook her head.

"Gee, I don't know – just ask me outright?"

"I can't do that. What if Mattie heard?"

"You think Mattie doesn't know what's going on when you say stuff like, 'Come and help me think of literary commentary in our bedroom and make sure to lock the door, because the literary commentary is just that exciting?' She's not stupid."

"Alright, well, next time how about I just yell, 'sex' and point upstairs?"

"Awesome – cutting straight to it, I love it. And then I can yell 'divorce' and point at the door."

"I will leave you one day. Find someone who's actually nice to me." The Doctor laughed.

"Coo, we both know, you don't want me to always be nice to you."

"Yeah, well, maybe I've got issues," Clara said, "Maybe I've got some deep-seated neuroses or self-hatred, and that's why I like it when you say so many awful things."

"Don't we all? Besides, you're not that screwed up. Now, River, on the other hand? And her handcuffs? Whips? That's neuroses for you."

"…Who was wearing the handcuffs, exactly?"

"I cannot divulge that information."

"It was you, wasn't it?"

"It's classified."

"Definitely you. You've never asked me to handcuff you."

"It's more her thing. I'm just, uh… willing to compromise. This isn't your way of telling me you want to get some handcuffs, is it…? Because they chafe."

"Erm, no. I'll just stick with us insulting each other. That's enough verbal intercourse for the moment."

"Gross! Did you just say 'verbal intercourse'!? That has to be the worst phrase anybody has ever come up with."

"Untrue."

"What's the worst phrase?"

"'Ofsted inspection'. 'Income tax'. 'I love you, will you marry me'."

"That last one? Really?"

"Sends a chill down my spine every time I hear it."

"I guess next time I'll say, 'Put on the damn ring, woman.' Probably make your knees go weak."

"You are complete and utter filth, I hope you know," Clara told her curtly.

"Filth are my politics, filth is my life."

"Shit. I might be in love with you."

"My pleasure."

"Shit."

"What? You're… still in love with me?"

"No, seriously, shit, look, ahead, at the station," Clara pointed.

Buckingham Central loomed out of the shadows, the train tunnel mouth opening up into the large cavern with its six platforms and dozen storefronts. Only now, it was overrun with plant life. Harvest-coloured leaves sprouted from the roots, drooping like vines from the high ceiling, forcing their way into the derelict shopfronts. None of that compared to what was right in the centre of the station, however; an enormous tree trunk, so vast it had broken through to the streets high above, though the mess of roots prevented any sunlight from reaching the underground. This largest tree burrowed into the concrete with more vast roots snaking out and into the surrounding tunnels.

That was when they saw their first kidnapping. A root twitched and retracted itself like a rubber band snapping, wrapping itself like a python around another human being, who didn't appear to be conscious. It happened too quickly for Clara to step in and do anything, and the root dragged its prey towards the central tree and then through a crevice in the ground and out of sight. It was a little like watching a chameleon catch a bug. The Doctor took off in pursuit, dragging Clara by the hand along with her.

"Let's follow it," she said.

"Erm, where?" asked Clara as they headed straight down the tracks towards the tree. The ground broke apart around the trunk, leaving passages deeper underground accessible. It was through these gaps they were apparently going to descend.

"Down! See where it's taking people! This is it, Coo, it's gotta be. This is the biggest tree I've ever seen in my life, and we went and saw General Sherman, do you remember?"

"No, what's General Sherman?"

"Earth's biggest tree. It's in California. Come to think of it, it might've been Amy I was with… but this one is bigger. Whatever we're looking for, I'll wager it's directly below this monster. The only question is how far below?"