Army radiation experiments awaken a subterranean monster from a fissure that feeds on energy and proceeds to terrorise a remote Scottish village. An American research scientist at a nearby nuclear plant joins with a British investigator to discover why the victims were radioactively burned and why, shortly thereafter, a series of radiation-related incidents are occurring in an ever-growing straight line away from the fissure.
Unfortunately the movie X the Unknown is not yet available on HBO Max.
| Writing | Jimmy Sangster | Screenplay |
| Directing | Leslie Norman | Director |
| Sound | James Bernard | Original Music Composer |
| Production | Jimmy Sangster | Production Manager |
| Editing | James Needs | Editor |
| Camera | Gerald Gibbs | Director of Photography |
| Writing | Jimmy Sangster | Story |
| Crew | Philip Leakey | Makeup Effects |
| Production | Anthony Hinds | Producer |
| Production | Michael Carreras | Executive Producer |
| Crew | Jack Curtis | Special Effects |
| Costume & Make-Up | Molly Arbuthnot | Wardrobe Supervisor |
| Directing | Christopher Sutton | Assistant Director |
| Costume & Make-Up | Philip Leakey | Makeup Artist |
| Camera | Len Harris | Camera Operator |
| Sound | Alfred Cox | Sound Editor |
| Directing | June Randall | Continuity |
| Sound | Jock May | Sound Mixer |
| Sound | John Hollingsworth | Music Director |
| Art | Edward Marshall | Art Direction |
| Camera | Mike Rutter | Clapper Loader |
