He hung in the Pit, ten miles down, tethered only by a thin cable. The mouth of the chasm was far, far above him, barely a pinprick of light. The lights around his helmet allowed him to see a few feet in front of him, but were nowhere near strong enough to penetrate the darkness below.

He wasn't scared, not exactly. There was the familiar rush of adrenaline, the one that followed him wherever he went – or maybe the one he had spent his long, long life chasing. But that same voice that had nudged him to volunteer to go down the lift with Ida, that had pushed him to insist he should be the one to explore the Pit, was now shouting that he should let go. Let himself fall. And somehow he wasn't surprised to find himself following it, as he unclipped one, then two of the three clasps connecting his harness to the cable.

His fear didn't come from the thought of falling. It was twenty miles above his head, in the base on the asteroid's surface. If he didn't survive this thirty-feet-or-thirty-mile drop – and the longer he stayed there, suspended in the air, the less sure he was about how much further there was to go – Rose was surely stuck there.

Ida was talking. Pleading him to stay, to be hauled back up to where she waited, so neither of them would be alone as they ran out of air. But he had to do this. Because louder than that voice was his never-ending desire to learn, to discover, to know. And what could ever be more worth knowing than whether there truly was a Beast, the precursor to every religion's story of the demon below? Whether there was existence before time, contrary to everything the Time Lords had ever known? Of course he had to go.

But there was one thing left – in case he was wrong, or unlucky.

'If they get back in touch,' he said. 'If you talk to Rose. Just tell her…' His breath caught, and he looked down, into the blackness that seemed infinite. How he wished he could speak to her, just one more time. Whether or not he survived the fall, there would be no way to get out of the Pit. 'Tell her –'

There were so many ways to finish that sentence. Tell her I'm sorry. Tell her thank you. Tell her she was brilliant.

So many ways, and yet only one that truly mattered. Something he'd never told her, not in so many words.

Did he really want the first – and only – time she heard those words from him to come from Ida, after he was gone?

His smart, fiery, beautiful, wonderful Rose. How he would miss her.

'Oh, she knows.'

He unclipped the final clasp, and he fell.

He had been certain that she knew. An hour ago, he would have staked his life on it. A minute ago, even. But now, as he fell through the dark into nothingness, down and down and down, he knew with a sudden clarity that it wasn't enough for him to think she knew.

I'll tell her, he vowed, hurtling through the air. If we get out of this, somehow, I'll tell her.

There was the Beast, and the Tardis, and the rocket, and the wild hope that Rose would figure out that the Beast's mind was on the rocket with her.

If anyone could work it out, it was Rose.

And work it out she did, breaking the viewscreen and releasing the Beast into space, leaving it to fall into the black hole, as its captors intended, should it ever escape. Her wild shout when she heard his voice made him smile, a twisting feeling in his stomach, as he realised she'd been as worried for him as he had been for her. When she returned to the Tardis, she practically launched herself at him, flinging her arms around him, holding him tight. He clung on to her just as tightly, lifting her off the floor. He buried his face in her hair, breathing her in – rose perfume, the metal of the station they'd just left, the strange cold smell of the black hole.

He finally set her down, pulling back just enough to look at her, to drink her in greedily. How could I not tell you, he marvelled. How could I almost die, and leave you stuck alone, thousands of years and billions of miles from home, without telling you this most important thing?

But not yet, because the comm was sparking – Zach checking Rose had left the rocket okay.

She flashed him a smile, then walked round the console to the comm. 'I'm fine, Zach! How's Ida holding up?'

'She's fine.' Zach's voice came through clearly, despite the damage to the rocket. 'A big groggy still, but she'll come to soon.'

'We'll leave her to your care, then,' the Doctor said, leaning over Rose's shoulder to speak. 'We're still a ways out from being safe from the black hole's orbit, so you might want to settle in for a bit.'

'Copy that.'

The comm went quiet. The Doctor nudged Rose with his shoulder. 'You couldn't help me out of this thing, could you? I don't particularly want to be wearing it all day, and I can't quite reach the fastenings.'

Rose grinned. 'You don't think the bright orange spacesuit is the epitome of comfort?'

A smile tugged at his lips. 'Shockingly, no. Give us a hand?' He gestured vaguely in the direction of the zips. Even flying the Tardis with the gloves still on had been something of a challenge.

She came up behind him and started unzipping and unclasping the different parts of the suit. As she did each one, her touch lingered just a second too long, as if she was trying to convince herself that he was real. She followed the line of zips around his shoulder, then undid the final panel. She drew it out of the way, her hand brushing over his collarbone as she did so, making him shiver.

'There you go.' She stepped back and crossed her arms. 'Should be pretty easy now.'

'Thanks.' He managed to extricate his arms from the suit, revealing his normal shirt and jacket underneath. His hands free, it was the work of moments to strip the suit off fully. 'I feel so light!' he said, bouncing on the balls of his feet. That drew his attention to the heavy boots. 'Well, apart from these things.' He kicked them off, leaving him in his socks.

He stared sadly at his feet. 'Goodbye, Converse.'

He could practically hear Rose roll her eyes and had to quash a smile. 'You literally have a locker of identical shoes – and a good thing too, the way you go through them.'

'Hey, this one's not my fault – I didn't know you'd leave the base before I got back and retrieved them!'

'So that's what, seven-two against you?'

'Do you have a scoreboard or something tracking this?' he complained.

'Ha! I should find one. Do you think if I ask nicely, the Tardis will show me where one's hiding?'

'Nope – she loves me too much.'

Rose raised an eyebrow. 'She's also got a sense of humour. I have a feeling this would be right up her street.'

He pointed a vaguely threatening finger at her. 'Don't make my Tardis choose.'

Her grin grew. 'Scared you'd lose?'

'Never.'

She laughed, her head falling back. The movement shifted her eyeline just enough to notice a small whiteboard that had materialised, as if by magic, against a coral strut behind the console, directly opposite them.

'No way.' Her face lit up, and she darted round the console to pick it up.

The Doctor noticed it a fraction of a second later, but he used his longer legs to sprint round the other side of the console to intercept her. He caught her by the waist, pulling her away from the whiteboard as their trajectories collided. She shrieked with laughter, making no attempt to escape, instead wrapping her arms around his and holding on as he clumsily manoeuvred them across the uneven floor. Finally they stopped, still laughing.

Rose leaned into him, her back against his chest, still in that half-embrace, breathless from laughing. 'I think I win that one.'

The Doctor was only half paying attention, most of his focus going towards fighting the urge to tighten his arms around her. 'I demand a recount.'

'For what? The board is right there.' She pointed, but when he turned his head to look, the board was gone.

There was silence for a moment. Then –

'You were saying?'

In retrospect, he might have said it a touch too smugly, because she elbowed him, and with his arms around her, he couldn't defend himself.

'Oof! What was that for?'

'Take a wild guess.' Her words were annoyed, but he could hear the smile in her voice, so decided he probably wouldn't be in too much trouble if he kept teasing.

'You must have been imagining things. The Tardis can't make things appear from thin air – she's a ship of science, not magic.'

Rose twisted round, an eyebrow arched. 'Imagining things, hm? Because if I remember correctly, you practically tackled me to stop me reaching it. What does that say about you?'

He smiled crookedly. 'That we're both going mad?'

She huffed a laugh. 'There are worse things, I suppose.'

'Yeah?'

'Yeah.' The way she said it was so certain, so definite, an echo of herself a day ago.

'Stuck here with you, that's not so bad.'

'Yeah?'

'Yes.'

The thought sobered him, and he let her go, heading back to the console to fiddle with something on the viewscreen.

There was quiet for a minute, though he could feel her gaze on him.

'Doctor?' she asked tentatively. 'When you were down there… what did you see?'

His head snapped up. She was looking at him steadily, but there was curiosity burning in her expression, which he understood. He had jumped into a bottomless pit to find the answer to that question, after all. No wonder she wanted to know.

'It was real,' he said. 'I don't know if it was the "true" Devil in a spiritual or religious sense, but it was something. Something that could certainly have inspired the stories of Satan, of the Pash-Pash Khullud, of Samael, of the Black Terror – the way it looked, the way it spoke, it all fit with the myriad descriptions of it from across the universe. And yet it was both more and less than all those stories. More in that it had a physical form – at least a hundred feet tall, red, with huge horns and fangs – but also great intelligence, and could take over a person's body, rather than just influencing their mind, and had more power than any religion is willing to give it. But also less, because the mystery of it is gone. It was just another creature – a powerful, immensely old and clever creature, but a creature nonetheless. It's like building a religion with a deity and its nemesis, but then you find out the nemesis was a dinosaur – huge and terrifying, but also just a being. An animal.'

'Do you think there is a Devil? Or its equivalent from some other religion? Both literally and metaphysically?'

The Doctor shrugged. 'There might be. And that might have been it. I never did decipher that writing. All I can say for certain is that it's gone now – the creature, that is. Its legacy – if you can call it that – remains, through millions of religions that heard whispers of that voice and knew to fear it.'

She tipped her head to one side. 'Did you fear it?'

He blinked. 'Of course I did. A being who claimed to be from before Time – how could a Time Lord not be scared of that?'

'So what made you keep going?'

Their gazes met and held, the moment catching, stretching taught. The Doctor had no words to explain, to describe what had happened in that cave, so he said nothing. He had sworn to himself that he'd tell her. He could talk for hours, ramble at a million miles an hour, but for this most important thing, he couldn't find the words.

After several long moments of silence, Rose looked away. He could see her biting her lip, clearly deep in thought. But just as she didn't press him, he didn't push her.

Eventually, she spoke again. 'Ida said you fell.'

'What?'

'When the radios came back online. She said you'd fallen into the Pit.'

He flipped a switch on the console. 'Yeah, I did. Well, technically I abseiled several miles down and then unclipped my harness, but you know, same difference.'

She shot him a look which said, You're babbling. It was true, so he stopped.

'She said – she couldn't stop you, but you said my name. What did she mean?'

He stared at the console without seeing it, just a haze of bronze and copper. 'She asked me what I believed in.'

He could feel her eyes on him, but he didn't look up. 'I dodged the question, of course – talked about how the Beast claimed to be from before the Universe, how that didn't fit with how I see the world.'

'But that wasn't your real answer?'

He glanced at her, taking in her frown, the set of her shoulders. Hesitantly, he shook his head. 'I said your name because I wanted her to tell you something. If – if I didn't make it back.'

Rose took a step towards him. 'She didn't tell me anything.'

'Because I didn't tell her.'

'Let me get this straight,' she said. 'You wanted Ida to give me a message, but then didn't give her the message to give to me?'

He stopped fidgeting for a moment, his head tipping back as he replayed his actions in his head. 'Well – yeah, I suppose I did.'

'That is the stupidest thing I have ever heard,' she said bluntly, but she was smiling as she said it. The Doctor grinned back, a quicksilver thing, melting a heartbeat later.

'It is, isn't it,' he agreed.

'So – what? You didn't want to give me the message after all?'

He let out a long breath. 'No, I did. I just didn't want it to come from Ida.'

'Yeah?'

She didn't press, said nothing more, but because she's Rose, she knew what he meant. Or at least, knew when he was talking around something, and that sometimes, the things he wanted to say were hidden between the things he didn't.

He changed tack, backtracking in their conversation. 'When I faced the Beast, I realised only its physical form was still trapped. Its mind –'

'– was possessing Toby,' Rose finished for him, unfazed by the abrupt change in topic, though there was still a little divot between her eyebrows.

'Right. And when I saw the rocket taking off, with you inside it, I realised what was happening. If I released the Beast, the gravity field keeping the planet in place would disintegrate, and it would fall into the black hole. But if its mind was separate, then its essence would live on, causing who knows what kind of chaos across the Universe.'

'Except I made Toby fall into the black hole too,' Rose said, understanding. 'Which meant both parts of the Beast were destroyed.'

'Exactly. But I had to take a risk, that you would figure out what to do. That you would be brave enough to do it. And you were. You saved the whole Universe from possibly Satan himself, and you did it thinking I was dead.'

Rose was looking at him blankly. 'I'm… not sure how this relates to your message to Ida.'

'Don't you see?' He crossed the distance between them in a couple of steps, so he was only a few feet from her. 'The thing I believe in – the person I believe in – is you. Always you.' His voice dropped from excited and energetic to serious and intent between one breath and the next. This was important. There would never be anything more important. 'I love you, Rose Tyler. And I believe in you, more than anything else in the Universe. Every Universe. Parallel and backwards and upside down.'

For a moment, Rose just stared at him. Then she smiled, slowly at first, until it took over her whole being. He'd never thought he'd see something brighter than a supernova, until he saw Rose smile like that.

She took him by the lapels, and with no more warning than that, pulled him into a kiss.

If her smile was a supernova, then her kiss was a burning star, scorching his skin wherever they touched. With a gasp, his hands moved to encircle her, to pull her closer. One of her hands slid up to settle at the nape of his neck, the other pressed against his chest, feeling his heartbeats racing.

Breathing hard, they broke apart, but only far enough to press their foreheads together. Their eyes met, and the Doctor was enraptured, even as he tried to piece himself back together after the force of that kiss.

'I love you too,' she said. She still wore that brilliant smile.

His breath caught. That she could say it so easily, without the nerves that had stilled his tongue all this time – it left him awestruck. 'You do?'

'Oh, my Doctor.' She brought one hand up to cup his jaw. He leaned into her touch, feeling it in every part of his body, right down to his toes. 'Wasn't it obvious?'

He thought of a thousand tiny moments: catching her looking at him and her gaze darting away; smiling brighter, wider than she ever had at Mickey; the heartbreak on her face when he'd regenerated into a stranger. The offer to share an ordinary life when they got off the impossible planet. The way she kissed his helmet before he left for the Pit. A hundred ways of saying it without words.

The same way he'd shown her. Intentionally talking nonsense around the Tardis, just to see if he could make her laugh. Reaching for her hand whenever they explored somewhere new, or were running from a monster, because he couldn't stand to be any further from her than he had to be. The way he couldn't say no when she made that one specific face: part mischievous, part hopeful.

Maybe he had known.

'Not obvious,' he said. 'I think part of me knew. The rest of me was just slower to catch up.'

'Obviously,' she said, amused. She brushed her thumb over his cheekbone, sending a shiver through him. 'I knew.'

'Well then, Rose Tyler, you're smarter than a Time Lord.'

'Knew that, too.' She grinned, and it felt like sparks were dancing across his skin. Without thinking, he leaned down and kissed her again. She kissed him back, winding her arms around him, holding him tight.

She knew. Of course she knew.

But it was nice to get to say it anyway.