| Director | William Peter Blatty |
|---|---|
| Budget | $2.5 million |
In the early 1970s, towards the end of the Vietnam War, a castle in the Pacific Northwest is used by the US government as an insane asylum for military personnel. Among the patients is former astronaut Billy Cutshaw, who aborted a Moon launch and was dragged screaming from the capsule, suffering from an apparent mental breakdown.
Colonel Hudson Kane, a former member of a USMC special unit, arrives at the castle to take over the treatment of the patients. Colonel Fell helps Kane acclimatise himself to the eccentricities of the patients. Kane eventually talks to Cutshaw, who refuses to answer why he did not want to go to the Moon. Instead, he gives Kane a St. Christopher medal. Lieutenant Reno, who is there attempting to stage Shakespeare plays with a cast of dogs, suspects that Kane is crazy himself.
Meanwhile, Kane constantly has nightmares of his brother Vincent, a former patient and murderer who is now dead. Cutshaw talks with Kane again, and they debate God and the idea of a divine plan. Kane, who believes that the existence of a God is far more likely than humanity's having emerged from "random chance", argues that deeds of pure self-sacrifice are proof of human goodness, which can only be explained by divine purpose. Cutshaw demands that Kane recall one concrete example of pure self-sacrifice from his personal experience; Kane is unable. Kane takes Cutshaw to a church service, which Cutshaw interrupts with several outbursts, and Kane momentarily hallucinates. After returning to the castle, Cutshaw thanks Kane and asks him to send him a sign as proof of an afterlife should Kane die first. Kane promises to try.
Kane then meets with a new patient who calls him "Killer Kane". Kane flashes back to Vietnam, where he killed a young boy. The soldier urges Kane to leave, and he screams. In the present, Kane collapses, unconscious. Fell explains to the staff that Kane is Vincent "Killer" Kane and suffered a breakdown in Vietnam. When Fell, who is Kane's brother Hudson, was dispatched back to America, Kane received the dispatch by accident. Kane created a new persona for himself – a healer, like his brother. Subconsciously hoping to heal people to make up for his "murders", Kane returned to the US as his brother. Realizing Kane's mental state, the Army psychiatric staff maintained the charade and sent him to Fell's hospital under the pretext of being its commanding officer. In reality, Fell has been the commanding officer all along. Kane awakens and remembers nothing of the incident.
Cutshaw escapes the castle and visits a bar. A biker gang recognizes Cutshaw from news reports and brutalizes him. A waitress contacts the hospital, and Kane arrives to retrieve Cutshaw. Kane humbles himself to the bikers to extricate Cutshaw, but the bikers are disgusted by his behavior and assault him. The gang attempts to rape Cutshaw, causing Kane to snap and kill most of them with his bare hands.
Kane and Cutshaw return to the castle, and the police arrive to arrest Kane for the murders at the bar. Fell interjects and tells the police officers that Kane must stay because he was provoked. Cutshaw later visits Kane. Dreamy and distant, Kane mumbles to Cutshaw about God and proof of human goodness before passing out. Cutshaw reveals that he did not want to go to the Moon because he was terrified of being alone in space. Cutshaw's admission appears to resurrect some lucidity within himself. As Cutshaw leaves, Kane's hand drops a bloodied knife. Outside Kane's room, Cutshaw notices blood on his shoe. Rushing back in, Cutshaw discovers that Kane had actually been injured in the bar fight and refused to get help, effectively committing suicide to provide proof of human goodness.
Some time later, Cutshaw returns to uniform and visits the now-abandoned castle. After reading a note left by Kane, which expresses hope that his sacrifice will shock Cutshaw back to sanity, Cutshaw finds a Saint Christopher's medal has somehow appeared in his car. He turns it over to confirm whether it was the one he gave to Kane and silently rejoices at what he sees.