At a NATO airfield in England, parachute engineer designer Jim Radford (Neil Connery) anxiously watches the testing of his new-style parachute with observers General Armstrong (George Sanders) and his aide Lt. Bailes (Michael Culver). The plane comes into sight and three paratroopers jump. For some seconds they fall through the air but there is something wrong - horribly wrong. The parachutes flutter towards the ground shapeless and twisted - and the men have disappeared.. A full enquiry is ordered by Whitehall and Bob Megan (Patrick Allen) a former special investigator is called in. An assignment which is to lead him into mysterious experiences... into the unknown.