Part one of three. Captain Jack Harkness throws himself back into the Doctor's life as the Time Lord tries to stop the Tardis hurtling out of control. Eventually the ship lands on a distant planet at the end of the universe, where a lonely professor is trying to save his people from extinction. Derek Jacobi (Gladiator) guest stars, with John Barrowman reprising his role from the first series and spin-off show Torchwood