Thank you, BBC iplayer for enabling me to watch this episode this morning. Hopefully everyone has now watched, if not, scroll down to the previous post.

79AD. The Doctor and Donna have arrived in Pompeii, thinking they were going to Rome, the day before Vesuvius is due to erupt. However, the soothsayers don't actually know it is happening and any suggestion that it might is false prophesy. (Don't you just love religious nuts!?)

The soothsayers are priestesses of Sybil, and breathe in the molten lava from Vesuvius which is turning them to stone. Or more specifically, into a legion of aliens who are using the volcano (or, for the sake of context, mountain) to power an empire that will take over the world. Not unlike the Roman Empire, really!

Anyway, The Doctor and Donna have to choose either, a) allow Pompeii to survive and the Pyroviles to take over the world, or b) end the Pyroviles dastardly plan and also all life in Pompeii. For historical continuity, The Doctor chooses the latter and cue stock footage of volcanos erupting.

Funniest bits in the episode.
1. The TARDIS being mistaken for "modern art", even the Roman Empire had it's fair share of poncey art types.
2. The household gods at the end being none other than The Doctor, Donna and TARDIS.
3. Saving the world, with a Water Pistol! Classic!