There are airborne viruses that are short-lived outside a host, Jim knows, but he figures the Doctor knows that, too. "Disease isn't enough to keep people hidden," he remarks, looking skyward. "Precautions can be taken to move around - there'd have to be some kind of legitimate threat to clear people out like--"

And then there's a noise, and the Doctor is off. Jim does not go for his phaser, valiantly, though the look he shoots Dorothy and the space between them in the TARDIS (just to check) is much more calculating than usual. "He's worse than I am," he mutters, and then moves, not wanting to lose sight of anybody.