With a cry, Sarah Jane ran towards her daughter's body and fell to her knees, cradling her. Two humanoid figures loomed in the doorway above her.

Sarah pulled a gun and fired at the nearest of the new arrivals, who shot her down with a gun he had already drawn. Noiselessly, Sarah crumpled on top of Vinny.

"Stand back!" cried the new arrival in a commanding voice. It was a woman, a short wiry woman in her thirties, dressed in a black and silver uniform. "Time agents! Stand back – no weapons!"

Behind her, much taller, came the second agent. "Don't panic people, they're only stunned. Drop your weapons or we will fire. And you wake up with a helluva case of pins and needles, so let's keep it nice."

It was Jack.

Rose thought she had no capacity for astonishment left, but other than the Doctor himself, Jack was the one person in the universe she was happiest to see at that moment. The fear and confusion she had pushed down overwhelmed her along with relief, and ignoring the pointed guns – ignoring the impossibility of the fact that he was here in this twisted, ghastly world – she broke from Adam's grip and threw her arms around him. "Jack! Oh, Jack."

"Hey," he said, sounding puzzled.

He smelled exactly the same, an exotic spicy very clean scent, as if he'd just stepped out of the shower and doused himself with alien aftershave. The clasp of his arms was incredibly strong, like arm bands squeezing her. She'd never got so far as full-on kissing him because he was such a whore she just hadn't wanted to go there, but it was so comforting to be held and find him just the same as ever.

"Captain!" snapped the female agent. "Do we have to have this kind of thing every time?"

"Sorry, ma'am, not exactly my doing." He loosened his grasp, but didn't quite let go for a moment. "Do I know you?"

"Yeah. No. I don't know any more, I'm losing track."

"We can fix that later," he said with a smile and his old half-wink, and released her.

"Rose, what's going on, who is this man?" said Adam, clearly perturbed and angry.

"I'm Captain Jack Harkness, this is Commander Gertrude Harrow of the Intergalactic Time Agency," said Jack.

"Adam Mitchell." Pointing her weapon directly at him, Commander Harrow advanced towards Adam, who backed away with a stumble and raised his hands. "You're under arrest by the Intergalactic Time Agency for gross and premeditated disruption of the timeline."

"What?" he squeaked.

"Captain." Commander Harrow nodded to Jack.

Jack took something that looked like a band of silver plastic from a pouch on his belt, grappled Adam – who put up a slight, ineffectual resistance – and secured his hands behind his back. "You don't have to say anything now, but anything you do say will be recorded and might cease to apply once the timeline is re-adjusted."

Adam's face was pale and panicked. "But I haven't done anything! Who are you? Rose – Rose – have you turned us in? Are you working for the Daleks?"

"The Daleks shouldn't be here," said the Commander. "Earth isn't even supposed to have fully established contact with other space-going species in this time period, or at least, the contact wasn't public knowledge. You've screwed up the history of your own planet like I've never seen before."

"You're going to take us to your time ship," said Jack, giving the band on Adam's wrists another tug. "We know you have one."

"You're mad! Both of you! I want to know that Sarah and Vinny are all right! And we're not alone down here. The others will come – "

"The others are sleeping peacefully as these guys, buddy," said Jack. "They made a fuss and now they're out of the action for now."

"Jack," said Rose, "he doesn't remember anything. He's part of all this now. He did do it, but he doesn't remember that he did it."

"Uhuh. What a fucking mess."

"Captain," said Commander Harrow. "Language on duty."

"Sorry, ma'am. But what're we gonna do now, if this joker can't tell us anything?"

"We'll just have to search for the signal of his ship. It must be somewhere nearby. There's some urgency, the stability of this whole timeline is degenerating. You, ma'am, perhaps you could explain why you seem to know what's going on, and how it is you know Captain Harkness."

"No," said Rose. "I couldn't." She glanced at Jack, then addressed the Commander, who was obviously his superior officer. "All I know is, this is all wrong. He – " she stabbed a finger at Adam – "took a friend of mine from time, somehow. I don't know how he did it, he didn't kill him, he removed him, he said."

"That's not possible," said Commander Harrow.

"It caused all this to happen. This is what Earth would've been now, in this time, if my friend never existed."

"Seems to me," said Jack, "that you know entirely too much."

Commander Harrow had taken an instrument out of her belt, the size and approximate shape of a mobile phone, and was pointing it at Rose.

"Can I make sure Sarah Jane and her daughter are OK?" Rose asked, directing the question at Jack.

He shrugged. "They're fine. Just stunned, like I said."

He made no move to stop her as she knelt beside the two women.

"Don't think about going for their weapons," Jack added.

"Don't be stupid," said Rose. "I need your help, why would I fight you?" Gently, she eased Sarah's body off Vinny's and laid her in a more comfortable-looking position on the floor, then clumsily felt for a pulse in both women's necks. One day soon, if she got out of this, she vowed she was going to take a first aid course. Watching TV had taught her well enough to do this much. She could feel the ripple of a pulse under the skin after groping a bit.

"She's of this time," said Commander Harrow, "but not of this timeline. Her resonance pattern's normal. We're going to have to arrest her too."

"Fine! Arrest me too! Just take me out of this place and help me get the Doctor back!"

"Who's the Doctor?" asked Jack.

"I thought you two weren't part of this?" She looked between them.

"We're not," said the senior agent, crisply. "Our time ship keeps us safe from temporal fluctuations, or we wouldn't be able to do our job at all. When we move outside our own time, we're protected anyway by the laws of time itself. Neither of us are native to this time period. You, on the other hand, are. Even if you were removed from time when the violation occurred, you ought to have been absorbed by the new reality when you were returned to it."

"Which seems to be what's happened to the perp," said Jack.

"So why don't you remember the Doctor, or me?" Rose said, and then the answer hit her. "You haven't met us yet. You're the old Jack. Time agent Jack, from before we met you."

"Shit," said Jack.

"Oh, well done, Captain," said his colleague.

"I hate this."

"Yet it keeps happening to you, doesn't it?"

"With respect, ma'am, this is not my fault!"

"It will be. But we've more immediate things to worry about right now. Let's take them both into custody and see if we can track Mitchell's ship in the vicinity."

"You can't do this!" cried Adam. "You're all mad! The Daleks will blow your heads off as soon as you go outside!"

"We don't need to go outside," said Jack, strapping another device around Adam's neck. It looked like a thing collar. He whimpered, but nothing happened to him. "If you don't mind, ma'am…"

Anxious to prove that she trusted him, Rose lifted her own hair and stood still as he fastened another one onto her. As his fingers touched the bare skin at the back of her neck, she shivered a little. She knew he was lingering a little longer than he needed to, and she felt him give her shoulders a small but firm squeeze, and a sweet, hot breath on her cheek. "My name's Rose," she said.

"I guessed. Pretty name."

"Cut it out, Captain," said Commander Harrow.

Jack stepped back with a grin. "Prepare to transport."

"How about – "

She was cut off mid sentence, a very disorientating experience. There was a blurry, buzzing sensation, and her new surroundings flashed into place with disconcerting suddenness. She stumbled and swayed, uncertain of the solidity of the floor beneath her feet.

"Whoa," said Jack's voice in her ear, and both arms gallantly and opportunistically supporting her.

Beside her, Adam clattered forward onto the ground.

They were in another space ship, small but bright and warm and clean. The interior was circular, the embracing hull dome-shaped, and they had materialised in a central area with soft seating and a table spread with books and empty cups. Around rim of the room were curved banks of instruments.

Commander Harrow immediately made for the controls, while Jack hooked a hand under Adam's bound arm to help him to the sofa.

"Oh God," said Adam, gibbering as he collapsed sideways into the slightly squishy seat. "Where are we? Is it a Dalek ship?"

"Do we look like Daleks, punk?"

"What about Sarah Jane and the others?" asked Rose. "We can't leave them down there!"

"Here's the thing. We're trying to repair the damage this jerk caused to the timeline. If we get things back on track, the timeline will revert to normal. Everyone in that bunker will go back to the way they should be, which I'm pretty sure, isn't hiding in a tunnel from a bunch of pepper-pot shaped alien invaders. They won't remember any of this."

"They won't remember," said Rose, slowly. Well, that was good. She felt uneasy about the idea of Sarah Jane waking up to memories of a life that, by external appearances, had been far more successful than the one she had really led, and a husband and children she no longer had. Vinny, of course, would cease to exist at all. She felt a flash of remorse at that, and her head began to throb with confusion. She had pressed her fingers to the living pulse in Vinny's neck, minutes before. She was still wearing her stinky old clothes.

"You've got to find the Doctor," she said, holding out a hand to Jack.

He took it. "Your friend, huh?"

"Yours too."

"Uh-uh, I do not want to know. The more I know, the more they wipe. I'm in enough trouble." He indicated his superior officer with a small toss of the head in her direction.

"They wipe your memory?"

"Yeah, parts of it, after mind-probing you. It's not fun. But it's the rules."

"Maybe – " She had been about to say, maybe that's what happened when they took two whole years of memories from your mind. It was what had caused him to leave the Time Agency in the end, as far as she understood it. But he didn't need to be given any more now to forget.

If he was going to be able to remember it, she was tempted to say to him - don't come with us when the Doctor says you can stay on the TARDIS. Or rather, hop off and find your own way at the first opportunity, because you are going to fall for the Doctor too and end up chucked overboard and forgotten. It wasn't fair. She had been so selfish and focussed. Now that he was actually here with her again, even if it was an earlier Jack, that feeling of remorse overwhelmed her.

The Doctor had lied. Bastard.

"Jack," she said, suddenly almost in tears, and hugged him again.

"How well am I going to know you?" he asked in her ear, pulling her closer. "I shouldn't ask, but hey."

"Not that well," she said, smiling through the tears.

"Pity."

"Excuse me," said Adam. "That's my girlfriend, if you don't mind."

"Yeah? Well, you're the one in handcuffs, bud."

"I'm not your girlfriend," said Rose. "But I'm not getting into that."

"Got it!" cried Commander Harrow, from the other end of the ship.

Jack strode over to her, and Rose followed. She was aware of Adam watching sullenly from his helpless sitting position.

The Commander had activated a little holographic pantomime of planets and speck-like spark objects, including a tiny detailed spinning disk that she imagined was the ship they were on. There was a flashing dot not too far distant from them, according to the graphic.

"It's definitely a void ship," said the Commander, absorbed in a read-out of information flowing on a screen below the hologram. "Well, it had to be."

"Any idea of its origin?"

"Nope. Unknown signature. We'll take this one in for analysis if we can."

"What are you going to do with Adam?" Rose asked, and the Commander turned to her with an irritated slightly surprised look, as if she'd forgotten she was there. "I mean, when he did this, he was sixty something. You can't put him back like he is now."

"Doesn't work like that," said Jack. "He's been crossing his own timeline, that's a misdemeanour in itself, if you don't have a licence to do it. The timeline disruption happened here, now, at this point in the space/time continuum. Doesn't matter that the perp came back in time to do it."

"He wanted to remove the Doctor five years before he ever met him, just to be sure," said Rose, thinking aloud. "But it changed everything, the whole course of his life, too."

"We find the exact moment the crime was committed, we fix the fault, we arrest the future version of him who committed the crime, and we return this guy to his proper time and place, where he'll re-integrate. Trouble is, we weren't expecting the perp to be so dumbass as to get caught up in his own changed reality. Usually when people pull this stunt, staying outside the changes is exactly what they aim to do, because they want something out of it."

"Well, that's what he wanted. To lead a normal life."

"I'm listening here," said Adam. "I can hear you, you know. I can't believe you're arresting me for something I haven't done yet, something I don't think I would ever do! And you, Rose, I can't believe you're part of this. You've always fought for freedom and justice!"

"Adam… I'm sorry… it's difficult to explain."

"Don't even try," said Commander Harrow brusquely. "Approaching the unidentified ship now."

"Don't feel bad," said Jack, in a lower voice, putting a hand on her shoulder. "We'll put him back where he should be and he won't remember a thing."

"And what you're going to do, it'll get the Doctor back?"

"If taking out your friend is what caused the damage, then sure."

"Perhaps," said the Commander, her eyes still on the controls. "We can't be sure of the collateral."

"What does that mean?" Rose asked in a moment of panic. Jack's fingers dug deeper into the flesh of her shoulder.

A musical tone sounded from the control panel. "All right. We're within transport range. There doesn't seem to be any shielding. Captain, get over there and find out what you can. I'll guard the prisoners."

"Commander, I'd like to take Rose with me. Since she can recall events, she may be able to help."

"I'll be honest here. At this moment I'm more suspicious of her than I am of Mitchell, whose timeline absorption seems genuine to me. I don't understand how she's retained her original resonance."

"All the more reason for me to keep a close eye on her, ma'am."

"Very well, but an eye is all."

"Would I?"

"Yes, you would. Get over there, and I want an ongoing status update. And Captain, don't blow it up. I want that ship impounded for the Agency."

Rose closed her eyes this time as the transporter beam took hold, and oddly this made it easier to balance when they landed. Jack reached out for her anyway, and squeezed her arm until it was obvious that she was steadied.

"You get used to it," he said.

Rose stood where she had materialised while Jack darted about to search their surroundings. Adam's time ship looked exactly as it had before she'd lost consciousness on the floor.

"Hmm, this isn't human technology, no way," said Jack. "The tech boffins back at base are going to have fun with this lot. Wonder what's this way. Stick with me."

"What are you looking for?" Rose asked, as they went beyond the control room where she had been held captive, to the corridor beyond.

"Trying to get a clue about what he did and how he did it."

"I told you what he did, he removed the Doctor from time, like the Time Lords were removed when they lost the Time War. Or maybe they didn't lose, I've never understood that – anyway, they're gone. And now he's gone too."

"The Time Lords!" Jack stopped and looked at her seriously. "I thought they were just a legend."

"No. They were real. But the Doctor is the last one."

"Are you sure about that?"

"What do you mean?"

"Come on Rose." He was much graver, even a little threatening. "It doesn't happen – humans who can withstand temporal disturbance. The Time Lords were supposed to have that power, it's part of the legend. I'm starting to wonder something here."

Without touching her, he had locked her physically against the wall, looming over her in a way that meant she would have to fight to get past him. She held still, and looked him in the eye. "I'm not a Time Lord, if that's what you're thinking. But I am pregnant."

"With the Time Lord's kid?"

She nodded. "I think the baby's protecting me somehow. It's maybe even protecting everything."

He broke into a wide smile, and threw back his head. "That is the craziest thing I've ever heard." He let her go. "Come on then, we'd better get its daddy back for you."

The corridor outside the control room was narrow, and curved sharply. Jack yanked open one door, which led into a tiny, neatly arranged cabin. He rummaged efficiently through Adam's few personal effects while Rose stood uneasily at the door. She was beginning to feel light-headed, a combination of shock, disorientation and lack of food – it must be several hours since she had last eaten, a delicious pasta dish at Sarah Jane's house in Chelsea. At least she was no longer feeling sick, which was something.

"Nothing of any use here," he concluded. "The guy doesn't seem to have had a life."

"No," said Rose sadly. "I don't think he did."

The next door along drew an, "Aha!" from Jack. It was a cupboard packed with what were evidently weapons. Jack removed a long, green, gun-like device which looked to Rose like something from a late-night cheesy B-movie – it even had Perspex-like rings along its barrel.

"This could be it," he said.

"What is it?"

"Wow, it looks like a portable null-device. Incredible. Usually these things are the size of a shopping mall." He tapped the communicator on his wrist. "Might've found the weapon, ma'am."

"Captain, I asked you for an ongoing status report."

"Sorry – but you're not going to believe this. It looks like a hand-held null device."

"That can't be right!"

"According to Rose, the rift was caused by Mitchell annulling a man called the Doctor."

"I find that unlikely. This amount of damage couldn't have been caused by the annulment of a single person."

"Actually, ma'am, from other information she's given me, I think it could. And he could've done it with this, if it's what I think it is."

"Well… review the ship's records to see if you can find when he entered the timestream to do this. My concern is that the timeline is so profoundly damaged in this area, we might not be able to get an accurate pinch point."

"I'll see what I can do, ma'am."

Two more cabins, which were entirely empty, and a tiny galley kitchen turned out to be the extent of the rest of the ship. They quickly found themselves back in the control room.

Rose looked around the place where she and Sarah Jane had been held prisoner while Jack pored over the instrument panels and pressed buttons.

"Do you know what you're doing?" she asked.

"No. Making guesses. I've never seen this technology before! I'm looking for the event recorder… if there is one… there's bound to be one…"

"He had a viewer thing, I can't remember what he called it, but he was able to show Sarah Jane – that's the woman he kidnapped with me, another friend of the Doctor's, the one you shot in the bunker – he was able to show her what she would've been doing now, in the old reality, before he'd changed things."

"Really! Now that would be handy. Oho, the Agency are gonna love this ship. Bonuses all round." He patted the console and grinned. "If we ever get this mess fixed."

"But couldn't you use it to see the moment when Adam did – whatever he did to the Doctor?"

"I don't see how."

"Your Commander woman was saying that the timeline was so messed up that you couldn't pinpoint it. Is that right?"

"Yeah, because usually we'd use a detector and a time viewer to spool back through time til we found the spot. There's too much noise here. We arrived at approximately the right place, approximately the right point in time, but we can't see where the damage occurred. We were relying on the perp to talk."

"Well, if you can see the old timeline by using the viewer on this ship, can you kind of - wind back?"

"It's worth a try," said Jack slowly, with a big grin.

Rose remembered why she had felt such an immediate connection with Jack when she'd first met him, and it had only incidentally been because he'd just saved her life. He really was like the Doctor, full of the same energy and delight. Like the Doctor, as she'd said, except with sex, too. Hah, well, that had been a long time ago.

It took Jack less fiddling about than she would have imagined to work out how to use the timeline viewer. From the help she could give him from what she could remember seeing Adam do, he located the bioscanner that had allowed the device to fix on Sarah Jane and extrapolate her alternative life.

"Sounds like what we really need for this is the wonder boy himself. But we'll try it out on you, Rose. Hold still, I don't want to put your eye out."

Rose held her breath, suppressing her nerves, as tendrils snaked down from the ceiling and touched her forehead. She opened her eyes, which she had closed reflexively, to find that Jack had already managed to get a picture into focus on the screen.

"Oh."

It was the untidy interior of her bedroom at home. The duvet was flung on the floor, all her drawers were pulled open and tipped out, and her teddies and soft toys were scattered everywhere.

"You're not there," said Jack. "Interesting."

"But that's my bedroom! My bedroom at home! It's still there!"

"No, it would be there. Nice housekeeping, by the way."

"I don't keep my room like that! It looks like we've been burgled or something."

"Hold still, I'm gonna see if I can scope backwards. Ah. Here we go."

Bizarrely, the scene in her empty bedroom started to spool backwards fast like a rewinding video. The door opened inwards and her mother – followed by the Doctor himself – reversed jerkily into the room.

"There! There!" Rose gasped. "Stop!"

The image slowed and began to run forward again, at normal speed. There was no sound, but it was obvious that the Doctor and her mother were having an almighty row. Or rather, Jackie was waving her arms around and yelling noiselessly, and the Doctor looked cold, tense, stressed. Then the Doctor began to pull the room apart, as if frantically searching for something or anything.

"That him?" asked Jack. "Cute guy."

Whatever he was doing, Rose didn't care. She gazed at the image of the Doctor ripping her cabinet drawers out and flinging her old teddies across the room with desperate relief and desperate longing. "He's there. He's OK."

"Rose, listen to me. He's not there. This is a phantom timeline. We have instruments that can detect outlines and resonances and this new technology here is superb, it's giving images – but that's all we're seeing. An image, an illusion."

"What – what can we do, then?"

"First of all, let's see if we can go back to the crisis point."

He set the image running backwards again. Her mother and the Doctor left the bedroom, now neatened, and they watched the empty bed for a while.

"I guess this is showing where you would've been," Jack muttered. "Faster, faster. This is the most boring bedroom scene I've come across in a while."

Despite herself, Rose snorted out a giggle.

The scene shifted to outside the flats at night, to the walkway where she had walked with the Doctor to tell him the news. And there they were, striding backwards.

"Stop!" cried Rose.

Jack had already hit pause and play, or the high-tech trans-timeline equivalent. She watched herself and the Doctor pacing along the concourse, looking painfully like an unhappy couple. The Doctor was hunched in on himself in that way he had, making himself a personal exclusion zone with his elbows and his shoulders and his hands thrust in pockets. She was walking a little too far away from him, her head bowed and her arms folded.

"Had a row, huh?" said Jack.

"No! Just a discussion."

They stopped, together, and looked awkward for a moment. The Doctor clasped her hands, leaned down towards her face, spoke with intensity. Rose saw herself smile and shake her head, and the Doctor planted a kiss on her forehead. She remembered how she had still felt uneasy and angry with him, and she hadn't invited him to kiss her properly. He never pushed that sort of thing.

The Doctor strode away – to the TARDIS to spend the night, of course – and the image tracked her as she wandered unhappily in the other direction, towards the staircase up to her mum's flat.

Jack shook his head. "Big row."

"No! Shut up, Jack. You don't understand."

"So you separated at that point?"

"Yeah. I went home, the Doctor went back to the TARDIS."

Jack made a frustrated noise. "We can't follow him now, this thing is locked on you."

The image of Rose climbed the outer staircase, looked over the balcony to where the TARDIS was – brooding, frowning – and turned into the flat.

"He didn't take the news about the kid too well?"

Rose folded her arms. "It's none of your business."

On the screen, she passed through the flat's tiny hallway, snapped at her mother, went into her bedroom and pulled a pillow over her head.

"Aww," said Jack. "That guy needs some lessons in how to treat women right."

Rose bit back what she might have said.

"Don't take this the wrong way, but I don't need to see you," said Jack, after another few moments. "I need to see him." He reached to fiddle with the controls, but stopped as Rose began to take off her clothes. "Hello."

"Oh, for God's sake, Jack."

"No, this is turning out to be a good home movie after all."

"Oi, look away."

"Think I've never seen a woman undressing before?"

"Well, you've never seen me undressing."

"I have now!"

To Rose's utter mortification, she was in the process of climbing into her old blue teddy bear print pyjamas, naked. And Jack was watching with a frank grin lighting up his stupidly handsome face.

She flicked out of existence.

"Whoa," said Jack, and rewound the moment. His expression was abruptly serious.

Once again, Rose saw herself pull the pyjama top over her head, and step one leg at a time into the bottoms. As she was drawing them up to her waist, she ceased to be there at all.

"I don't remember that happening," said Rose in amazement.

"You don't remember putting on your pjs?"

"Yeah, I do – kind of – then I just got into bed and went straight to sleep, I think. When I woke up in the morning, that was when things were different."

"It looks as if things were different right there, only you didn't realise it. That's the moment. You crossed into the new reality. So Mitchell annulling your boyfriend – must've happened right there, right then."

"He probably never got as far as the TARDIS."

"What's the TARDIS, his ship?"

She nodded.

"If it's a void ship, like this one and ours, that's likely. It would have been hard for anything to get at him there." He punched his communicator. "Commander, I think we've got a pinpoint on the exact moment. I'll explain later how – you've gotta see this stuff."

"Good work, Captain. We need to hurry, stability is down to twenty-three percent."

"We should bring Mitchell over here and hook him up to the machine, it'll let us see for sure."

"Get back here with the temporal co-ordinates in the first instance, and I'll make a decision on that."

"Understood, ma'am." He turned to Rose. "Ready?"

"Just a moment." Something had caught Rose's eye. On the floor, half concealed behind a protruding panel, was a small black device that was obviously shaped to fit around a humanoid hand. She recognised it as she picked it up.

"Hey, careful!" said Jack, immediately taking it from her. He dangled it from one finger. "Nasty. You don't want that to go off accidentally."

"Is it a gun?"

"It's a cellular disruptor. Yeah, it's a gun, and it's not one of the better ways to die."

"I was shot with it."

"You were what?"

"Adam. He shot me with it. At point blank range. It made a kind of blue light, and I felt numb – but it didn't hurt. It knocked me out though. I think it's the same one, he must've dropped it."

Jack looked at the hilt of the gun and said, "OK."

"OK?"

"It's on its lowest setting. You were lucky, three or higher and your internal organs would be soup." He pressed a switch on the gun and slipped it into his all-encompassing belt, then activated his communicator and spoke with a new tone of urgency. "Commander, forget what I said just now – we need to get straight in there and make the pinch. I think we could be running out of time."

"You're telling me! Stability's fallen to seventeen percent! You've got an estimate on the co-ordinates?"

"A pretty accurate one, I reckon."

"I'll trust your judgement on this one, Captain. Transmit them to me and get down there now."

"What's happening?" Rose asked, suddenly scared by the change in his demeanour.

"Change of plan," said Jack, without meeting her eye. "Hold on tight – let's go and find your Time Lord."