After an attack on moonbase an amazing discovery and a wild theory are resultant.
The body of the alien examined was found to be human in origin, totally, not just with human organs transplanted.
The theory - Dr Doug Jackson proposes the possibility that ,
" the aliens can take over our bodies, transmit to it their own purpose, or imbue it with an alien intelligence. Perhaps they have no bodies at all, and need us as vehicles, the form of life they take I can't begin to wonder"
Straker " meantime keeping these 'human computers' alive with organ transplants"
Meantime Jim Regan, SHADO astronaut has Earth leave and is driving in the countryside with his wife, when suddenly a Siamese cat in the road makes him break swiftly. Nearby landed in the field is a UFO.
Before he can react two aliens grab him and his wife and cart them off to be medically examined inside the craft. Jim awakes at the roadside, his wife and the UFO gone.
His wife presumably going back to homeplanet to be organ fodder, Straker relieves Regan of duty to recover from the shock.
But that darn cat!...Regan has it with him at SHADO HQ, whenever he picks it up he develops head pains, the cat glares at him, mentally controlling him. It runs around loose at HQ taking great interest in the control room.
Foster is due to go back to moonbase to fly a SHADO interceptor craft to escort the Venus Probe, but he is ambushed in the car park by Regan and thumped unconscious. Regan while pummeling Foster makes cat like meows and scratches Foster's face.
Foster recovers and tells Straker what happened, but its too late, Regan is flying the interceptor, he has disabled Interceptors 1+ 2, which were accompanying him.in space flanking the Venus Probe, they are now stalled as Regan flies interceptor 3 directly on collision course for moonbase.
Straker is told about the cat seen wondering around, and with Regan's cat like meows whilst attacking Foster, pieces it together.
More..