At the sound of Rose's voice, both men whipped their heads towards the doorway. Rose stood there, looking fresh-faced and bright-eyed. She figured she'd gotten about four hours of sleep, which was at the high end of what she tended to need in recent years. She'd then showered and gleefully changed into her old favorite pair of jeans and her most comfortable hoodie. A pair of battered trainers completed her lazy-day comfort look.

Rose wished she could say that her two men were so enthralled by her that even in such unimpressive clothes she could send them into a shocked silence, but given what she'd heard Jack say as she walked in and her earlier suspicion that they were keeping something from her, she was certain she'd have to be content with simply surprising them. She smiled warmly, ready to put the screws to them if need be.

As she stepped into the room, the Doctor took large steps to meet her. "Well, when he says that, he means – shouldn't you be sleeping?"

"Don't think you'll get 'round me by playing that rambly-Doctor interruptin' yourself game, Doctor." She poked him in the chest and brushed past him. "And you," she said, crossing to Jack. "Don't think you can play innocent, I've seen too much of you to believe it when you get that look on your face."

She put her hands on her hips and turned so she could aim her glare at both of them at once. "You've been keeping something from me since the library. Maybe you didn't want to talk about it in front of Martha or maybe you had things to work out, but she's not here right now and I am not prepared to give you any more time." She looked expectantly at each of them in turn. "Well?"

"No, really," the Doctor said, acting as though she hadn't said a word. "You were exhausted, I know you, I could tell." He was in front of her in three paces and took her face in his hands, peering curiously into her eyes.

"Oi!" she exclaimed. "I'm not a specimen!" She jerked backwards but laughed good-naturedly. "I just don't need that much sleep these days."

The Doctor stared at her for a moment and then nodded. "Can't say I'm surprised."

Rose sobered when she heard the tone of his voice. Perhaps this was more serious than she thought. "Doctor, what is this about? You said I was healthy, were you lyin' to me?"

"I think you should sit down," he began.

"I will not! What's wrong with me? Doctor?"

Jack reached out and grabbed the sleeve of her hoodie and tugged her over to the bench. "Sit with me, baby doll. You're fine," he assured her. "I promise." He glanced at the Doctor, hoping that they were right and he wasn't going to be proved a liar. "Just sit with me, okay?"

Rose glanced from Jack to the Doctor and nodded slowly. "Fine. But you tell me everything, okay? Don't leave anythin' out – and I will be able to tell if you do."

The Doctor glanced at Jack, who slung his arm behind Rose's shoulders and shifted an inch or two closer to her.

"Rose," the Doctor began, "other than needing less sleep lately, have you noticed anything else… different about yourself?"

Rose blinked. All this over not needing as much sleep? But then, the Doctor hadn't known about that until a moment ago, so it couldn't be the problem, even if he hadn't been surprised by it either. Jack and the Doctor were looking at her very seriously, so rather than laugh off the question or give a flippant answer, she did honestly try to think of something.

"I'm sorry," she said. "No, I can't say that I have."

"Have you looked in the mirror, Rose?" The Doctor brushed a tender finger over her cheek. "When I say that you haven't changed a bit – haven't aged a bit – since the last time I saw you, I'm not just being polite, or kind." He dropped his hand from her face and patted the console. "And earlier, in the library, you told me how the TARDIS was feeling, like you just knew. How did you know?"

Rose looked at Jack. She was confused by the Doctor's line of questioning. "What's he on about?" she asked Jack, trying to keep her voice steady. He tucked a wayward strand of her hair behind her ear and mustered a smile for her.

"When the Rift was opened in the Hub, there was debris flying everywhere. Everyone had cuts and scrapes over their faces and hands when it was over." His crystalline blue eyes were more serious than Rose had ever seen them. "Everyone except me," he paused and took her hand, "and you."

Rose's eyes widened. "What are you saying?" she whispered. She whipped her head back around to look at the Doctor. "Doctor? What are you saying?"

"Rose, we think – well, I say 'think,' but we know, really, because I wouldn't say this if I weren't at least 95.6758% sure that it were true, because if I were wrong it would just be such a mess, and-"

"Doctor!"

At Rose's exasperated exclamation the Doctor shut his mouth abruptly. "Sorry," he said after taking a breath. "What I meant to say was: do you remember the golden light from the heart of the TARDIS?" At Rose's nod, he continued. "That's huon energy. Normally, it's only found inside the TARDIS – it's an essential part of the process that allows the ship to harness the Time Vortex and move through it. When you opened the console and absorbed the Vortex, you must have absorbed huon energy first, which then allowed you to manipulate both the Vortex and the TARDIS."

Under Rose's unblinking stare, he paced agitatedly. He pulled his brainy specs out of his pocket and slipped them on without even thinking about it. "When I took the Vortex out of you, I must have left behind some of the huon energy. Slowly, your cells must have then adapted somehow, because now you're literally soaked in it."

The Doctor stopped pacing and faced Rose. "And there have been some residual effects."

"When you say 'residual effects,'" she murmured, squeezing Jack's hand nervously. "Is it hurting me?"

The Doctor sat down on her other side and took her free hand apologetically. "Rose, some of the tests I did on you before were to do with those effects, and as far as I can see, you really are as healthy as a horse. Everything I know tells me you should be dead, but nothing I've found so far is detrimental to your health; in fact, it appears that it's actually making you healthier. You traveled through the void and only felt a little dizzy. You only need a few hours of sleep to feel refreshed." He gestured at Jack. "You appear to be as impervious to minor injuries as Jack is."

Rose looked over at Jack, wide-eyed. "No cuts, like you. Like you," she repeated. "Oh, God."

"Let's just hope the opportunity to test whether or not you're as impervious to death as I am never arises," Jack put in.

The Doctor squeezed her hand again. "I don't know if you're immortal like him, Rose. You might be, or you might just have an extended life span."

"How extended?"

The Doctor shook his head. "I don't know. I don't know if something like this has ever happened before. I've certainly never been in this situation before and if there was any Time Lord who was ever going to get into this situation, well, it was probably always going to be me, so I don't even think there'll be anything in the library." He glanced at the Gallifreyan display on the monitor. "Even if Gallifrey weren't gone, I don't think the Time Lords would know for certain."

"You're one of a kind, Rose Tyler," Jack said, smiling.

Rose gave a half-hearted laugh. "Or maybe one of two." She took a deep breath and let it out slowly. "I suppose it won't be too long before one of our adventures is death-defying enough for me to find out."

The Doctor grimaced. "Or perhaps I can figure things out with a little bit of testing and comparison in the med bay."

"Won't that be fun?" Jack said dryly.

The three of them sat in silence for a few minutes. Jack still had his arm over Rose's shoulders, and when the Doctor had sat down next to her, Jack had rested his palm lightly against the Doctor's back. The Doctor still held one of Rose's hands.

"Am I still human?" she asked suddenly.

The Doctor shrugged, took off his glasses and slipped them in his pocket. "Is Jack?" But he smiled comfortingly. "I know you hate tests, but as I said, there are a few I'd like to do once we've solved our current dilemma – cell tests and DNA mapping. It won't hurt."

Rose nodded. "I understand." She smiled at him weakly. "I trust you."

The Doctor smiled back at her, leaned in and kissed her softly. "Thank you."

Rose patted the Doctor's hands with her free hand and then did the same to Jack's knee. "So I suppose you two have been figurin' all that out rather than figurin' out how to fix what's wrong with the TARDIS, then?"

"Actually," the Doctor replied, "we've been multi-tasking. Well, I say multi-tasking. Really it just so happens that I'm fairly certain you are the key to fixing what's wrong with the TARDIS."

"What?" Rose sat up straight and stared at the Doctor in surprise. "I learned a few things about alien tech at Torchwood, but the TARDIS is way more than a little beyond me."

The Doctor got to his feet and rocked idly back on his heels. "Under normal circumstances, I'd agree with you on that. No offense." Rose shook her head absently, waiting for him to continue. "But when you and Jack came on board, the TARDIS reacted, and that's why we're stopped," he emphasized the word, drawing it out and widening his eyes pointedly, "in the middle of space. First she reacted to Jack – that's why she lit out of Cardiff like she was terrified of something. But then she reacted to you."

"Me? But I didn't do anything!"

"Neither did Jack. But the energy you're giving off – the TARDIS recognized that, she recognized you, and so she stopped."

"Okay," Rose said, trying to take the startling information about the after-effects of the Vortex in stride. "Even if that's true, even if it was my presence that stopped the TARDIS, that still only leaves us stopped in the middle of nowhere."

Jack shifted next to Rose, pulling back the arm that had been resting behind her and gently holding both her shoulders with his hands. She moved her gaze from the Doctor to Jack, the question still in her eyes. "We think – well, the Doctor thinks and I agree – that the huon energy you're giving off, and the fact that it came from this TARDIS in the first place, gives you a stronger connection to her than you had before."

"If you embrace that, if you harness that," the Doctor said, picking up the thread of Jack's explanation, "then I think you should be able to tell her that Jack's all right and she can just go back to Cardiff."

"Why can't you? She's your ship, isn't she?"

The Doctor frowned. "She won't listen to me," he mumbled, thinking to himself that taking only the best was all well and good, until they were smart enough to pick up on things you'd rather they just missed. "You're the one who told her to stop, even if it was subconsciously." He shrugged, embarrassed at the fact that his ship wasn't listening to him. "So you're the one who has to tell her to go again. It's just a small recalibration, really."

Rose thought about it for a moment. "What if it doesn't work?"

Jack kissed her temple. "Let's cross that bridge if we come to it."