Fires of Pompeii
Generally, the episode revolves around The Doctor and companion Donna landing in Pompeii on the day of it’s destruction.
They meet a few locals, who the immediately bond with, and that’s when they discover it’s d-day for Pompeii.
The Doctor hurries Donna along to the Tardis so they can get back home before they become just another part of the death toll. Donna has other ideas. She wants to find a way to save the city. Admirable, if a bit cocky.
The Doctor explains about fixed points in time. It’s a story we’ve heard before—and accepted. Donna, however, is not willing to accept it. A rebel, shouting ‘why?’ Shouting. Hollering. Nagging.
When he doesn’t give in to changing history, she begs him to at least save the family they met. He’s reluctant. Even their end is part of the fixed point in time.
And that’s one of the unique elements of this episode. He goes against his judgement. He saves the family.
The other aspect of this episode that makes it important is the casting. An extra on the streets of Pompeii turns out to be Karen Gillan, who will later go on to fill the role of Amy Pond. That’s an easy one to miss. The role is small and there’s make-up involved.
Even bigger than that, Pete Capaldi is in the episode as the father of the family they save. Four seasons later, he’d take the roll of the 12th Doctor.
In the middle of some inner turmoil, the 12th Doctor begins rambling about his face. Why was it chosen? It wasn’t random. He had it for a reason, etc, etc. He puzzles out that he chose that face to remind him of the time he saved a family from dying in Pompeii. It was a reminder that he saved people, and that he should save people.
It’s a clever connection, but I wonder if they had that in mind when the offered Capaldi the role. Perhaps they didn’t think anyone would notice…