Donna's entire world collapses, but there's no sign of the Doctor, as Russell T Davies's Bafta Award-winning time-travelling drama continues. Instead, she finds help from a mysterious blonde woman – a traveller from a parallel universe. But, as Donna and Rose Tyler combine forces, are they too late to save the whole of creation from the approaching darkness?

David Tennant plays the Doctor and Catherine Tate plays his companion, Donna Noble. Billie Piper guest stars as Rose Tyler.