Moonbase 3

Dr Helen Smith becomes concerned over the mental state of pilot Harry Sanders. She expresses her feelings to the base's second in command, Michael Lebrun, and tries to convince him to get Commander Ransom to remove Sanders from duty. Ransom refuses and assigns Sanders to pilot the Commander's shuttle for a trip to Earth. After an malfunction, Sanders cuts the communications link and goes outside the shuttle to make repairs and is thrown into space. When Ransom attempts to pilot the shuttle it explodes. The European agency sends a Welch scientist to take over the station and to investigate the shuttle accident.

After a number of mysterious deaths, paranoia sets in as the crew begins to believe the deaths are being committed by a 'Moon Monster' living on the surface of the Moon.

The station's crew suffers from an unusual number of accidents and mistakes. Caulder must deal with the problems while trying to operate within his Earth-bound superiors' budgetary limitations.