 " The Fires of Pompeii " is the second episode of the fourth series of the British science fiction television series Doctor Who . It was broadcast on BBC One on 12 April 2008 . Set shortly before and during the eruption of Mount Vesuvius in AD 79 , this episode depicts alien time traveller the Doctor ( David Tennant ) and his new companion Donna Noble ( Catherine Tate ) on a trip to Pompeii , where they uncover an alien invasion . Their clashing worldviews present an ethical dilemma for the Doctor . 
