The Fires of Pompeii

The Tenth Doctor tries taking Donna Noble to ancient Rome for her first trip in the TARDIS, but seems to have miscalculated. Instead of seven hills, they find a single mountain billowing smoke — Vesuvius. They're in Pompeii, 23 August 79 AD: the day before "Volcano Day". However, something else is horribly wrong. The Soothsayers' predictions seem to always be correct... so why can't they see tomorrow's disastrous events, the eruption of Vesuvius, the death of their city? What is blocking their perception, and will the TARDIS team be able to walk away from a fixed point in time, saving no one from certain doom? Well, Donna has something to say about that!