First Broadcast on 3rd December 1978
Executive Producer James Gatwood
Produced by Sidney Hayers
Directed by David Pick
Adapted by Gloria Tors
Guest starring:
Michael Hinz, Maurice Kaufman, Martin Potter, Aimee Delamain, Ian Collier, Catherine Brandon, Maureen Morris, Samantha Weysom & John C Williams.
Julian, Dick, Anne, George and Timmy the dog go off to Wales for a holiday. As they near their destination Uncle Quentin takes a wrong turn leading them to a building called Old Towers atop a desolate hill. They intend to ask for directions but are deterred by locked gates and a fierce guard dog. While exiting, the car inexplicably feels heavier, as if the brake is on. Upon reaching Magga Glen, they are greeted and fed by the owner, Glenys Jones and meet her son Morgan.
Timmy gets into an altercation with three of the farm dogs and is bitten by one of them. Upset, George promptly resolves to leave the next day. Julian and Dick climb the hills and find the farm's guest chalet. They also encounter the shepherd's young daughter, Aily.
George is dissuaded from leaving when the children opt to spend the rest of their holiday in the chalet. They enjoy their first day there, but at night strange rumbling sounds, vibrations and a shimmering light emanate from the hillside. The next day, they see a woman's face in a window at Old Towers.
Aily befriends the Five and shows them a note, thrown from a window of Old Towers by the elderly owner, Mrs Thomas. The note states: "I want help. I am a prisoner here in my own house, while terrible things go on. They have killed my son. Help me, help me!
Julian and Dick show the note to Morgan, who takes it from them and orders them not to interfere. His attitude causes the children to suspect he is a villain.
Aily takes the Five to to Old Towers. They locate Mrs Thomas, who tells them some evil men murdered her son, Llewellyn, and are exploiting a rare metal beneath the hill in order to make bombs. Back underground, the children spot Morgan and the shepherd and observe the subterranean mining operation. All of them are caught by the villains, who are led by Llewellyn Thomas. Morgan breaks free and calls his dogs, who come to the rescue. Back at the farm, Julian telephones the police. Morgan later returns with the shepherd and says the villains have been jailed. The group then celebrates Morgan's birthday.