The Doctor and his friends Ben, Polly and Jamie arrive at Gatwick airport. They quickly stumble upon an alien plot, centring upon the mysterious ‘Chameleon Tours’ - a low-price holiday company, whose young passengers have been vanishing in unexplained circumstances. The Doctor investigates further, but it isn’t long before his own friends start disappearing too.

• BBC Studios
• Patrick Troughton
• Anneke Wills
• Michael Craze
• Frazer Hines