The TARDIS makes a hazardous return to contemporary Earth, materialising at Gatwick Airport in the path of an oncoming aeroplane! The travellers split up in order to evade airport security, but in doing so they become embroiled in a plot to steal the personalities of young human beings.

The Chameleons: faceless aliens who have lost their very identities following a disaster on their home world. Now they have infiltrated the airport, setting up the bogus Chameleon Tours in order to kidnap passengers and take over their very identities. As the Doctor and his companions become mixed up in the alien machinations, it soon becomes difficult for them to distinguish friends from enemies....

This story, only two episodes of which survive in the television archive, marks the departure of companions Ben and Polly, played by Michael Craze and Anneke Wills, from the series. It also features Frazer Hines as Jamie and Pauline Collins as Samantha Briggs.