Maria and her dad, Alan, dig deeper into the mystery of Luke's new parents and discover that Luke has actually been kidnapped by the Slitheen. There are more shocks when Sarah Jane and Maria find out that Mr Smith, Sarah Jane's supercomputer, is one of the bad guys. With Clyde 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?