Trainee doctor Martha Jones thinks this is just another ordinary day at the hospital, that is until the Judoon invade and teleport the building to the surface of the moon. Searching for a fugitive from the law, the intergalactic police force start scanning the patients for non-human DNA. This puts one of Martha’s patients into action but she cannot understand why Mr. John Smith keeps telling her that he is the Doctor and while he might not exactly be from Earth it isn’t him that the Judoon are looking for.
The Doctor finds himself with a new companion, Donna – but she’s late for her wedding! As the Tardis races to get to the church on time, the mysterious Empress joins the chase, and it becomes clear that Donna is the key to an ancient alien plan to destroy the Earth.