The movie was adapted by John Huston and John Lee Mahin from the novel by Charles Shaw and directed by Huston. It was nominated for Academy Awards for Best Actress in a Leading Role (Deborah Kerr) and Best Writing, Screenplay Based on Material from Another Medium.
Corporal Allison (Robert Mitchum), a U.S. Marine, is a survivor of a failed island scouting/reconnaissance mission in the Pacific during World War 2. Allison and his team were in the process of being deployed from a U.S. Navy submarine when they were discovered by Imperial Japanese Navy warships. In the confusion of battle the submarine captain takes his ship below the surface to evade enemy fire, leaving the scouting team behind. After days of being adrift in a rubber raft Cpl. Allison arrives on an island and finds an abandoned settlement and a chapel with one occupant: Sister Angela (Deborah Kerr), a novice nun who has not yet taken her final vows.
For a while they have the island to themselves, but then a detachment of Japanese troops arrives to set up a meteorological camp, forcing them to hide in a cave. When Sister Angela is unable to stomach the raw fish Allison has caught for them, he sneaks into the Japanese camp for supplies, narrowly avoiding detection. His long absence frightens the nun, who is just about to surrender herself when he finally returns. That night, they see flashes from naval guns being fired in a sea battle over the horizon.
The Japanese unexpectedly leave the island, and in both celebration and frustration, Allison gets drunk on some sake left behind. He voices his frustration that he loves Sister Angela and that he considers her devotion to her vows to be pointless, since they are stuck on the island "like Adam and Eve." She runs out into a tropical rain and subsequently falls ill; Allison, now sober and contrite, finds her shivering with chills. He carries her back but sees that the Japanese are returning in much greater force, and is forced to hide them in the cave again. Allison sneaks into the Japanese camp to get some blankets for her. He kills a soldier who discovers him in the act, but that alerts the enemy to his presence. In an effort to force him out into the open, the Japanese set fire to the vegetation.
Allison and Sister Angela are left with two choices: surrender or die from a hand grenade. Sister Angela prays for Allison, who wields his Ka-bar, waiting for the inevitable attack. However, the ensuing explosion is not a grenade but a bomb; the Americans have begun attacking the island in preparation for a landing. Allison comments that the landing will not be an easy one because when they returned, the Japanese brought with them four artillery pieces whose positions are well-concealed.
In what he attributes to a message from God, Allison decides to disable the Japanese artillery during the barrage, while the Japanese are still in their bunkers. He is wounded, but manages to sabotage all the guns, saving many American lives.
Allison and Sister Angela say their goodbyes as they await rescue by the Marine assault troops. He has reconciled himself to her dedication to Christ and she reassures him that they will always be close "companions".
Huston's two leads are instantly believable, with Kerr having cinema experience as an Irish nun in Black Narcissus and Mitchum as a Marine in Gung Ho! (1943 film). The screenplay compares the rituals and commitment of the Roman Catholic Church and the United States Marine Corps. The Catholic Church Legion of Decency monitored the production of the film closely, whilst the Marines provided troops for the invasion climax.