The Doctor, Lester and others in “Revenge of the Cybermen”

[while examining an infected man who's going to be shot by his comrades] The man is sick, he needs treatment!

Lester

There is no treatment. All we can try to do is stop the infection spreading!

Sorry, gentlemen, I can't allow it.

Commander Stevenson

You can't allow it?

My colleague is a doctor of medicine and I'm a doctor of many things. If we could examine him-

[interrupting him] Commander, I'm afraid we have to kill these people, too. They brought the plague in here.

Who's the homicidal maniac?