Ten and Donna arrive in Pompeii one day before the eruption of Mount Vesuvius. Twelve immediately steals the TARDIS and while trying to get it back some soothsayers arrive and soothsay the shit out of everyone. The Doctor fights off some fire demon with a water pistol, Donna gets captured, they meet the Pyroviles, but eventually the Doc and Donna get bored and decide to trigger a volcanic eruption which destroys the entire town and slaughters thousands of innocent people. Ah, much better.
Quite good. If Capaldi wasn't in it no one would remember it tbh.