After all was said and done and the Doctor had saved the day again, Rose sat on the floor of the TARDIS, hugging her knees to her chest and watching the Doctor fiddle around with the sonic screwdriver while humming a merry tune. She couldn't get the image of her head of the Doctor sprawled out on the floor right where she was sitting, unconscious, only one heart beating. Dying. A vague thought meandered its way into her mind and she blurted it out, only half-thinking.
"We need an Infirmary." The Doctor glanced over his shoulder.
"A what?"
"An Infirmary, you know, like a proper hospital place." The Doctor's expression mildly resembled someone who had been slapped with a fish – taken aback and just a little disgusted.
"Now, why in the whole wide time vortex would we need that?" Rose rolled her eyes.
"In case one of us gets sick or injured, or…I dunno, a regeneration thing gone wrong again, there's no telling what could happen." The Doctor shut off the sonic screwdriver with a satisfying little snap and turned to face her with his manic grin.
"Ah, but you're forgetting! I'm a Time Lord, Time Lords don't get sick. Two hearts keep a lot more blood flowing to the immune system. Takes a hefty plague to wipe us off our feet! None of those pesky sniffle things you humans always get."
"Alright then." Rose conceded, ignoring, for the moment, that he hadn't said it was impossible for him to get sick, only that it would be difficult. "But I'm human, remember? I get sick. I get hurt. And I don't exactly have a sparkling track record when it comes to keeping out of trouble." The Doctor frowned and she knew she had made her point.
"You made a promise to my mum, right?" she barreled on, sensing weakness. "You said you'd protect me, well I don't see how you can protect me without proper medical supplies." She paused for a moment to let that sink in before she delivered the final blow. "You are a doctor, aren't you?" His face flushed and she knew she had hit the jackpot. He hated when people doubted his ability as a doctor, medical or otherwise.
"Fine, alright then!" He threw up his hands and pretended to be annoyed, but secretly he was pleased. If Rose was requesting an Infirmary in the TARDIS, that meant she was planning on staying for a good long time. Enough time to get into trouble, anyway, which usually didn't take her very long.
The TARDIS began to tremble before he had even finished the thought. It shuddered, bubbled, and seemed to expand right before their eyes, drifting out of focus as it did so. When everything became clear again, there was a door that hadn't been there before, a plain brown door marked with a golden plaque. "INFIRMARY", it read, just in case they hadn't guessed.
"The TARDIS works fast." Rose remarked, and the Doctor laughed.
"Come on, Rose!" he cried joyfully, taking her by the hand. "Let's explore our new Infirmary – and let's hope we never have cause to use it."