The Runaway BrideS00E04

Bride-to-be Donna vanishes as she walks down the aisle to marry boyfriend Lance. To her complete astonishment - and the Doctor's - she reappears in the Tardis. As the Time Lord, still reeling from Rose's departure, investigates how Donna came to be there, the duo uncover a terrifying enemy. How far will the Doctor go to save Earth from the latest alien threat?