10 Greatest "I'm Dead And I Know It" Moments From Modern Doctor Who
2. Donna Noble - The Fires Of Pompeii
The Fires of Pompeii is an excellent early episode for the Doctor and Donna. It also introduces both Karen Gillan, who would later play Amy Pond, and Peter Capaldi, who would of course return as the Twelfth Doctor. This story was a harsh lesson for Donna, as she learned just how painful it can be, to be a time traveler who can't change the big disasters of the past.
As the volcano begins rumbling over the city, Donna does everything that she can to warn people, though the Doctor tries to stop her. Then, they stumble into the mystery of the Pyroviles, a race of aliens who are attempting to convert Earth to a new homeworld, after their's was lost. If they succeed, all of humanity will be wiped out. To stop them, the Doctor and Donna must reverse the effect of their machines - though that will directly cause the eruption.
At this moment, Donna, fully believing that this will be her last act, places her hands on the Doctor's, and together, they flip the switch that sets off the eruption. While they thankfully survive, this was the first example of her committing to self-sacrifice, though of course, it wouldn't be her last.