"The Hour That Never Was" is the ninth episode of the fourth series of the 1960s cult British spy-fi television series The Avengers, starring Patrick Macnee and Diana Rigg. It originally aired on ABC on 26 November 1965. The episode was directed by Gerry O'Hara and written by Roger Marshall.

Steed and Mrs Peel swerve to avoid a dog and crash into a tree. The clock in the car smashes and stops just before 11 o'clock. Steed knows the area well and the two set out on foot and visit the old RAF base. They enter the lounge and find it set for a party but everyone is absent. They do not yet notice that the clock has stopped at 11 and the fish in the tank have frozen still. Outside they find a car with petrol flooding and nobody attending to it. The other buildings of the base are empty and a milk cart abandoned. Seeing the name Geoffrey in the book, they visit his quarters and also find it empty and an electric shaver still running. They find the air control tower empty and then spot the milkman fleeing across the tarmac who is shot dead.

Looking for the culprit, they find a rabbit alive but unconscious, and later the body of the milkman disappears. Steed and Mrs Peel separate and investigate the base further. Mrs Peel discovers the body of the milkman on his float as a deafening shrill noise and quake shakes through the base. When the noise eventually stops, Steed returns to the lounge to get himself a drink at the bar, whereupon he discovers the frozen fish and stopped clock. Outside he discovers a vagrant looking in the dustbins. Steed gives him a drink in the lounge and the vagrant says he also experienced the shrill noise. A dog enters which belongs to the gate tender and is known to the vagrant. Steed approaches the gate house and is struck unconscious by a falling barrier.

The scene then returns to the crashed car and Steed emerging from it as if the crash had just happened. Mrs Peel is missing. Steed returns to the base and finds the lounge bustling with activity; he is greeted by old comrades. They tell Steed that Mrs Peel had rung them telling that she was unable to attend, and they say there is no tramp living on the premises. Outside he discovers the dog who leads him to the dead body of the tramp, just as the milkman drives off (with the body of the original milkman on the back). The milkman takes the body into the cook house. When Steed approaches he finds the apparently dead milkman alive and well and busy. The milkman and an accomplice take out new bodies from the medical centre and put them on the back of the float. Steed investigates the clinic. He overpowers a guard and discovers Mrs Peel tied up and unable to recall anything since the accident. Looking at the equipment, Mrs Peel surmises that the people in the airbase had been hypnotized and programmed to potentially create sabotage. As Steed plays with an ultrasonic device the people in the lounge hear the shrill deafening noise over the speakers as he and Mrs Peel realize that is what has happened.

...
Wikipedia