Moonbase interceptor pilot James Regan is on 48 hours leave from the
Moon. He and his wife are invited by an older couple, the Thompsons, who have mysteriously been given an unusual psychic
board game. While the two couples are playing the game, Regan starts to have strange reactions and faints. Later, as Regan and his wife are driving down a country road they stop their car to avoid a
Siamese cat. They are then abducted by aliens who take them to their
UFO, where he has another experience similar to the one he had at the Thompson home. Regan awakes back in his car with the cat but his wife missing, abducted by the aliens. Regan explains his story at SHADO Control but Straker sends him back to the Moon. Meanwhile the cat now has free rein inside Control. SHADO's resident doctor –
Douglas Jackson – has performed an autopsy on an alien body and found it to be entirely human, not – as previously believed – an alien species that harvests human organs to extend its lifespan. He surmises that the aliens may be able to control human brains. When piloting his
SHADO Interceptor escorting the
Venus probe, Regan fails to destroy a UFO that leaves Earth carrying his wife. He is recalled to Earth for an assessment. Still controlled by the cat, Regan attacks
Col. Paul Foster and returns to the Moon, where he puts his interceptor on a crash course with Moonbase. Straker determines that the cat is controlling Regan and has it eliminated. No longer under alien control, Regan sacrifices himself by just missing Moonbase but is unable to avoid impacting on the lunar surface. ==Regular cast==