Goofs

Wyngarde's gun is heard to fall on the beach, but appears on the table again in the rest of the scene.

When Drummond is on the bed in the castle Penelope remotely turns off all of the lights in his room but when she opens the door to the room the lights are all on.

At the end of the film, Drummond (Richard Johnson) and Robert (Steve Carlson) dive off the yacht and swim away from the boat towards Grace (Suzanna Leigh), who is in the water. But as the film cuts to a long shot and the final credits roll, they are still swimming towards her - but from the other direction, moving towards the boat.

The harpoon hits the table surface as shown in a close-up shot, but later on in the scene it is in the side of the table.

When Drummond takes the small piece of tape over to the reel-to-reel deck, he takes out a tape splicer. The camera cuts to Carloggio for a brief sentence, and as the camera pans to Drummond, he has already spliced yellow leader on both ends of the tape, which would take at least a couple of minutes.

Elke Sommer, playing Irma, jumps out of a plane with parachute. Her hands and feet are bare. But in the following free-fall she has white gloves and white shoes on, obviously her stunt double.

The gate to the castle is seen falling second before the car runs into it.

Wyngarde's gun is clearly pulled away by a string some time after the harpoon struck the table.

When Drummond takes the piece of tape, it is about 6" long. This piece of tape likely came from one end of the original spool and would not be long enough to contain any audio.

When Drummond and his nephew are driving down the coast road to stop the bomb going off, they comment that it' s five to twelve i.e. five minutes to go. They then drive all the way into the town, capture the two assassins, obtain a motor boat and land on the yacht at 11.58. Impossible.