When The Doctor, Sarah and Harry arrive in Scotland, having received an urgent request for assistance from the Brigadier, they discover that the mysterious force which has destroyed three oil rigs has left giant teeth marks on the wreckage.
The mystery deepens leading them to the shores of Loch Ness where they find that the legendary monster really does exist – and it’s the murderous tool of the Zygons, aliens intent on overpowering the planet.
The Doctor and his companions must find a way to defeat the deadly Loch Ness Monster and its controllers, but the Zygons have the terrifying power to change shape and the Doctor is in grave danger when he finds that his friends and allies are not always what they seem…
This story had working titles of: Loch Ness, The Secret of the Loch, Secret of Loch Ness, The Loch Ness Monster and the Zygons.
This story was originally planned to end Season 12, but was pushed back to the start of Season 13 in order to allow the series to shift its broadcast schedule from a January start (as had been the case since 1970) to September Although debate has arisen regarding a later delayed-broadcast story, The Next Doctor, regarding what season it belongs to, no such debate appears to exist regarding Terror of the Zygons which, despite its production schedule, is universally considered part of Season 13.
Radio Times credited John Woodnutt as Duke of Forgill for Part One, Broton for Parts Two and Three, and Broton/Duke of Forgill for Part Four. All on-screen credited read Duke of Forgill.
This marks the only time one companion who had already been with The Doctor before anotherone joins remains with him after the second companion leaves, with the exception of Katarina and Sara Kingdom, who weren’t there very long, and ended up dying. Generally, The Doctor’s rosterof companions revolves fairly consistently.
