American scientist Brain Donlevy sends a rocket with three men into space; it comes back with only one and he is very, very sick. What happened to the other two - the ship was hermetically sealed? Well this decent British sci-fi/horror film follows the investigation as together with police officer Jack Warner they try to get to the bottom of things. Meantime, the sole survivor of the exploratory flight goes awol and we discover an alien creature is now on the loose on post war London and it is hungry! It's now race against time to stop it reproducing and taking over the world - and who better ...