The TARDIS materializes on 1996 Earth at Gatwick airport.  Polly sees a murder and is kidnapped by the murderer.  Ben, soon after, also vanishes.  The Doctor and Jamie try to tell the authorities about the events with little success.

They find out that many people have vanished and all of them from a tour company called Chameleon Tours.  The Doctor and Jamie team with one of the vanished persons sister to investigate.  They find that the missing people are being replaced by the alien Chameleons who have lost their identities and need to take on new ones from the missing people.  The Doctor offers to help the Chameleons and they release the humans.

Ben and Polly learn that they are on Earth on the same day that they originally left and they decide to stay.