Maria (Yasmine Paige) and her dad, Alan (Joseph Millson), dig deeper into the mystery of Luke's (Tommy Knight) new parents and discover that Luke has actually been kidnapped by the Slitheen. There are more shocks when Sarah Jane (Elisabeth Sladen) and Maria find out that Mr Smith (Alexander Armstrong), Sarah Jane's super computer, is one of the bad guys. With Clyde (David Anthony) nowhere to be seen, Luke in the clutches of aliens and no Mr Smith to help, things are not looking good for Sarah Jane and Maria. But just what do the Slitheen want with Luke? And who, or what, exactly, is the Xylok?