Gravely wounded following a daring nighttime commando raid, Captain Craig Killian (John Loder) returns to England to the closest hospital, a private sanitarium, to treat his injuries. Little does anyone suspect that Killian has been intercepted by Nazi spies who secretly run the sanitarium the same nest of spies whose secrets Killian uncovered on his mission. Killian, dubbed the Gorilla Man for his uncanny climbing ability, demands to be released in order to deliver the intelligence to high command. But the dastardly Nazi doctors hatch a desperate scheme to discredit Killian, claiming he received a brain injury and is delusional. When Killian escapes the hospital, the Nazis take their evil plan a step further, framing him for a brutal, psychotic murder. Now a fugitive in his own land, Killian will risk it all to complete his mission.