The Doctor had equipment that could analyze DNA in a matter of minutes. He wasn't quite sure why he'd told Rose that it would take significantly longer than that. Perhaps he felt a need to cover his bases; if he found anything indicative of contact with the werewolf, he'd need time to figure out what to do.

When the small computer in the lab beeped at him and he read the results, he was glad that he had given himself those additional hours. He checked the samples for the second time, frowning as he did, then moved to another section of the lab to remove some vials and beakers. He knew what needed to be done, but he wished there were another way…

Nearly three hours had passed before he was ready to tell Rose the news. He walked down the hallway with quiet steps then paused before her door. It was ajar; she always trusted him, even when she was asleep.

He swung open the door. She lay upon her stomach on the bed, partially covered by her pink duvet. Her hair was spread out on the pillow, and one hand lay beside her cheek. In sleep she looked like a child. For a moment the Doctor stood watching her, and he wondered why he had ever invited her to travel with him. She was so young, so vulnerable… But she was strong, too, and bold, and she never backed down from a challenge. Those were the traits that would see her through the next few difficult days.

He sat down on the bed and rested his hand over her back. He could feel her heart beating, a perfectly normal resting rate of 55 beats per minutes. He could sense her body temperature with his palm, and it was also well within the expected range. He ran his hand over her glossy, thick hair. She was healthy, which was very good just now.

Gently he shook her shoulder as he spoke her name. She required a minute or so to rouse, blinking sleepily at him and gathering her bearings. She was still very tired; she had slept perhaps four hours after more than twenty-four of wakefulness. Still, he needed to tell her what he planned to do.

She turned over and sat up, rubbing at her eyes. "'S mornin' already?" she asked, forgetting for a moment that there was really no such easy division of time on the TARDIS.

"Not quite," he smiled at her, "and I'm sorry I had to wake you, but I need to tell you the results of the DNA analysis."

Suddenly Rose jerked to full alertness. All traces of stupor left her, and she reached for his hand automatically. Now her skin felt cold.

"What is it? What did you find?" she asked.

He kept her hand in his. "There were traces of protein containing foreign DNA—"

"So it did scratch me," she finished, the color draining from her face.

"Possibly. But hair is also made of protein, and it could have just been a bit of fur that got into the wound."

"But if it was the claw, then I'm… I'm going to become like him?"

The Doctor squeezed her hand. "No, Rose, you aren't."

"But if it got any of its DNA in me, it'll multiply an' take over, an' change me, right?"

"Not if I can help it." He grinned at her. "And I can!"

Rose blinked. "Really?"

"Yep." He reached into his pocket and withdrew a syringe. "I synthesized a vaccine. It'll prevent the cellular mutation and in essence turn your own immune system into a big ol' fightin' machine that'll knock out the other DNA."

"You did that?" She was clearly surprised.

"Told you, I'm very good."

She smiled. "Yeah."

His pleased expression began to fade. "Thing is, Rose," he began.

"What?"

"You know that when you get a vaccine you're receiving a very weak form of whatever disease you're trying to prevent. It kick starts your immune system into producing antibodies to fight that disease, effectively tricking it into creating permanent defenses. But since you've been given the disease, albeit in a very small and diluted form, sometimes you feel a little ill for a few days. Happens to babies and toddlers all the time…"

"Right. I've seen that with my cousins."

"Well, this vaccine," he glanced at the syringe, "works the same way. I was able to create a very weak form of lycanthropism, which your own immune system will fight off."

Rose froze, her hand gripping his tightly. "So you're sayin' that I'm going to have to become a werewolf for this to work?"

He almost laughed at the huge and inaccurate leap in logic that her little human brain had made. "No, Rose, not at all. You shouldn't have any of the external symptoms. But you're going to feel it inside. You watched that poor creature change. You saw the first signs—increase in metabolic function, for one."

"So I'm not gonna sprout fangs, claws, and nasty hair all over?"

"No."

"Then what's the big deal?"

"I'm afraid that you won't feel very well for a day or so."

"Like how?"

"Fever, some aching, probably muscle cramps—that sort of thing."

"So I'm gonna feel like I have flu?"

He nodded. It wasn't really a bad analogy, although he knew that it wasn't entirely accurate. Still, if it helped her to understand and accept the situation, he decided that there was no need to correct her and cause her worry.

"Think I can handle that." She pushed up the sleeve of the nightshirt she wore. "Go ahead."

He smiled in gratitude. He had been afraid that he'd have to explain more, to tell her details he'd rather she not find out, at least not until she had to. He took a small, packaged antiseptic wipe from his pocket and tore open the foil. He rubbed the pad over her arm then removed the cap from the syringe.

"Hey, wait a minute," she said.

The Doctor's hand froze. "Yes?" he asked as casually as he could manage.

"I thought you said needles were twenty-first century. What's with that?"

He exhaled in relief. "Sorry, Rose. It's still the most effective way to get this into your system."

She shrugged. "Go on, then."

He injected the vaccine into her arm, rather proud of himself for his very light touch. She felt no pain. It was the least he could do for her, really. He pocketed the empty syringe then stood and offered her his hand.

"'M still pretty tired," she said. "Think I'll just go back to sleep for a little longer."

"Nope, come on. Up and at 'em. I want you to have something to eat."

"I'll eat later," she began.

He took her hand and pulled her up. "No time like the present. I'll make you my famous scrambled eggs with cheese. Lots of nice protein, calcium, and vitamin E."

Rose cocked an eyebrow at him. "What, no potassium?"

"Ah, potassium. Good idea. You'll have to have a banana, too."

She stood by the side of the bed. She seemed to be waiting for something.

"Come on," he urged.

"I'll be there in a few minutes. Just let me get dressed."

"You don't need to do that," he said, then wished he had kept quiet.

She looked at him quizzically. "Why not?"

"I think you should go back to bed after you've eaten," he answered rather quickly. "Get some more sleep. No need to waste time getting dressed if you're just going to get undressed again." He grabbed her robe from a chair and held it out to her. "Besides, dining today's going to be very informal."

She took the robe and slipped it on. "Can I at least run a brush through my hair and splash some water on my face?"

"All right, but hurry. My eggs taste best when they're just out of the pan." He gave her a wink then left the room, the plastered-on smile fading as soon as he entered the hallway.