Trama

Paul Roper is a SHADO technician with a pretty, younger wife and aliens have threatened to kill her unless he passes on to them cryptic computer co-ordinates, the possession of which will allow them to make an undetected attack on the Moonbase. Colonel Freeman discovers what Roper has been doing and Roper asks for the opportunity to make amends by undertaking a dangerous mission to the Moon to stop the attack.—don @ minifie-1

SHADO does not trust anyone in a way. Psychology tests take place continuously in order to check that all staff keeps on being loyal. They especially measure stress, nerves, etc... However, not everybody believes in the necessity of such tests.

Paul Roper (George Cole) is a technician which works in the UK headquartes of SHADO. He's married to a pretty and much younger wife, Carol (Sonia Fox), who has been lately receiving weird threatening phone calls. She's become a bunch of nerves. One day, she points her husband's shotgun to the door because she thinks it's the person who is making the threatening calls, which puts Paul inthe situation of betraying SHADO to protect his wife. He's told her that, when he spoke to the police, he was told that it was a burglar who used to commit crimes in their neighbourhood, but that he's been trapped. It's not even necessary for Carol to testify in the police station.

Roper starts feeding cryptic co-ordinates to the aliens, the possession of which will allow them to make an undetected attack on the Moonbase. Colonel Alec Freeman (George Sewell) has a short conversation with Paul in the corridors of the hidden SHADO base, and realises that Paul is under a lot of stress. He and Comander Ed Straker (Ed Bishop) interrogate him and test him on the stress level. They discover that Roper is a traitor.

Straker devises a plan to release Roper and follow him. However, Roper is freed before time. The aliens attack him while on his way home to his wife's arms. Carol is terrified once again and she picks up the shotgun. However, she is killed.

Roper is attacked but survives. He is distraught because Carol had died. He will carry out a dangerous mission on the moon on behalf of SHADO. He waits for the UFO which will follow the coordenates he's been feeding them and will shoot the spaceship on sight. He succeeds, but is killed on the process.