The setting is an island prison, somewhere in French Guyana, a place that's clearly supposed to be Devil's Island. Verne (Gable) is a thief who keeps repeatedly trying and failing to escape, rather than just serving out his sentence, because that's the kind of guy he is. In desperation the warden gets him a laboring job outside the prison walls in an effort to tame him. That backfires, as he meets Julie, who has arrived at the island to work as The Chanteuse at the local cantina (and maybe also as a prostitute). Verne makes another bolt from prison in order to find Julie and do the horizontal mambo with her, but when he breaks into her room, she calls the cops and he's sent back inside. Despite calling the police, Julie is ordered by the island's governor to leave forthwith for having a convict inside her room. She rejects the attentions of M. Cochon aka "Pig" (Peter Lorre), but miscalculates and winds up as the prisoner of another islander, Marfeu.
Back in prison, Verne muscles his way in on another escape attempt. A hardened, vicious prisoner named Moll has arranged to have a boat laid up on the beach. His party, including Moll's innocent young friend Dufond, cultured wife-poisoner Hessler (Paul Lukas), and a couple of other prisoners, will bust out and make a run through the jungle. They attempt to ditch Verne, but he takes advantage of the chaos caused by their escape and makes a bolt on his own as well, liberating Julie from Marfeu along the way.
Moll's party is assisted by Cambreau (Ian Hunter), a prisoner who just sort of appears in the jail, without anyone knowing how he got there. The gentle, kindly Cambreau has an uncanny knack for knowing where to go, what to do, and what's going to happen. He also has a habit of staying with the prisoners as they start to die off during their escape attempt, helping each one to find spiritual peace and redemption as they go. And there's that one time his voice sounded inside Julie's head, when he wasn't even there, as she was about to kill a man...
Eighth and last film pairing of Gable and Crawford.
- The Alcatraz: A Devil's Island style prison.
- Day Hurts Dark-Adjusted Eyes: Verne is left wincing and squinting when brought out into the light after thirty days in solitary confinement.
- Face Framed in Shadow: When we're introduced to Verne, in his isolation cell, he's all in darkness except for a beam of light illuminating his eyes.
- I Never Told You My Name: Hessler is the first to pick up on how there seems to be something otherworldly about Cambreau when Cambreau calls him by name, and Hessler notes that he never told Cambreau his name.
- Jungle Drums: Heard from the natives. The natives are never actually scene, but one of the prisoners is found dead with arrows in his back.
- Lover and Beloved: A surprisingly overt depiction of this with the very manly, intimidating Moll, who nevertheless is tender and affectionate to his smaller, vaguely effiminate companion Dufond.
- Messianic Archetype: Eventually it becomes clear that Cambreau is a Christ figure and may in fact actually be Jesus Christ. Verne is able to make good on his first escape attempt when Cambreau somehow just pops up among the work detail, leading the guards to get a full count of 36 prisoners despite Verne's absence. Verne knows Hessler's name without being told. When they're on the escape, Cambreau has an uncanny ability to know where to find water and food. He's also always there to offer succor and comfort in dying men's final moments. He talks about redemption and how God is within everyone. He doesn't seem to suffer from exposure and thirst. The climactic moment with Verne comes after Verne has knocked Cambreau off the boat and Cambreau is clinging to driftwood, in a manner reminiscent of Christ on the cross. And then there's how his voice sounds in Marfeu's little hut, saying "Not that way, Julie" as she's about to assault Marfeu, even though Cambreau isn't there in the room.
- Quicksand Sucks: Verne plunges into some quicksand, but surprisingly is able to escape quickly, by grabbing a vine.
- Redemption Rejection: Hessler has figured out that Cambreau is apparently something supernatural, and that he seems to be bringing the prisoners to moments of spiritual redemption. Hessler, who states directly that he's going to get back to the work of marrying and poisoning gullible ladies, specifically rejects Cambreau, saying that Cambreau's "little victories" won't mean anything if they aren't accompanied by defeats. Cambreau says they'll never see each other again (because Hessler has chosen the way of sin). Hessler leaves the cabin, then pauses outside, doubt filling his face. Then he says "no", and stalks off.
- She's Got Legs: Verne bursts into Julie's room as she's taking off stockings.
- Suck Out the Poison: Kindly Cambreau does this for Telez after Telez's leg has gotten infected and is swelling up. Another prisoner points out that it won't actually do any good, to which Cambreau answers that he knows it won't, and the point was to show to Telez in his last moments that someone cared about him.
- Tap on the Head: Moll, who doesn't want Verne tagging along on their escape, whacks him on the head with a shoe (which apparently had something in it to make it a better weapon). Verne is still unconscious hours later, but somehow has no lasting ill effects.
- What, Exactly, Is His Job?: It's unclear just what Pig is up to or why he's on the island. This is part of the vagueness regarding sexual matters enforced by The Hays Code, but it seems that Pig is probably meant to be some sort of pimp, who wants to use Julie as a prostitute. When Pig tries to return the reward money and instead get the order ejecting Julie from the island cancelled, the warden angrily shoots back that he doesn't deal in women.