Humphrey Bogart plays Frank McCloud, a World War II veteran who visits a shoddy, run-down hotel in Key Largo, Florida, that has been taken over by a notorious gangster named Johnny Rocco (Edward G. Robinson). Rocco is waiting at the hotel to conduct business, and awaits the first chance to flee to Cuba where he'd been exiled by the feds.
The hotel is run by the disabled James Temple (Lionel Barrymore) and his daughter-in-law Nora (Lauren Bacall), the widow of Frank's old friend. James mourns the loss of his son in Italy and wants him to have died a hero. A passing sheriff's deputy, checking on the place as a hurricane threatens to blow in, is also taken hostage by Rocco's gang. A group of local Seminoles try to find sanctuary but are forced to huddle outside as the storm approaches.
The hurricane arrives before the gang can do business and depart, and the mobsters are trapped with the hostages as the hurricane hits shore.
This film provides examples of:
- Affably Evil: Curly is so polite and upbeat that you almost forget he's a mobster.
- Affectionate Pickpocket: Gaye hugs Rocco to steal his gun.
- Arch-Enemy: Johnny Rocco to Frank McCloud.
- Bloodless Carnage: Common for the period, the climatic shoot-out is perfectly bloodless, even without bullet holes. The only blood on-screen comes from Sawyer's head wound.
- The Bully: Rocco is this way to everyone, even to his own Mooks and alcoholic girlfriend Gaye. The hurricane shows that Rocco can be more of a coward than the people he bullies.
- Closed Circle: Thanks to Hostile Weather, the main characters are trapped in one place for the entire movie.
- Cue the Sun: The second to last scene of Nora opening the blinds to let the sun in after the hurricane has passed.
- Diagonal Billing: Robinson's and Bogart's credits are shown this way, with Bacall's off to the right.
- "Die Hard" on an X: One of the earliest film examples. However, while the characters are held hostage in an isolated environment for the bulk on the film, Frank doesn't get to sneaking around and knocking off bad guys until they're on the boat towards the end.
- Dirty Coward: Nora derides McCloud as this after he says he won't risk his life just to bring Rocco down. It's subverted later on when she sees McCloud risk his life just to comfort Gaye after Rocco torments her.
- Played straight with Rocco himself, however. He's brave enough when he has people outnumbered or the other guy's gun is unloaded, but when faced with real danger, such as the hurricane, he quickly loses his nerve. In the final face-off with McCloud, he pleads, begs, and tries several times to trick Frank into dropping his guard.
- Don't Explain the Joke: Toots is called out on his habit to explain his jokes.
- Dramatic Thunder: More often than not does the thunder strike at a pivotal point in the narrative.
- Expy: Rocco is loosely based on Lucky Luciano, one of the most powerful gangsters of the 1930s who ended up imprisoned in 1936 and then deported to Sicily by 1946. Like Rocco, Lucky Luciano tried running his crime empire from Cuba for a while, after he was kicked out of the United States.
- Film Noir: Key Largo is considered one of the defining noirs.
- Forceful Kiss: Rocco plants one on Nora, she later returns the "favor" with a Spiteful Spit.
- Hostile Weather: A hurricane plays a pivotal part in the movie.
- I Lied: Rocco promises Gaye a drink if she sings but refuses to give her one once she is done.
- In Name Only: All that the film has in common with the play it is supposedly based on is there being a couple of fugitive Seminoles falsely blamed for a murder. The characters of the play have completely different names and backstories. The play does not feature a gangster taking people hostage, and is not set during a hurricane or even in a hotel, though its Spanish Civil War background was out of date by the time the film was produced.
In fact, director John Huston disliked the original play so much, he barred Jerry Wald (the producer who'd convinced Huston to adapt it to film in the first place) from the set during filming completely.
- Ironic Echo: Rocco spends most of the movie armed and dangerous, threatening to shoot the hostages on the slightest whim, taunting Frank as a coward for surviving the war. When the hurricane starts turning Rocco into a quivering mess, Frank taunts back: "You don't like it, do you Rocco, the storm? Show it your gun, why don't you? If it doesn't stop, shoot it!"
- It's Always Sunny in Miami: Averted with the hurricane striking the island.
- It Works Better with Bullets:
- Rocco gives Frank a gun and taunts him to take a suicidal shot at him, saying that a real hero should be willing to die to rid the world of Johnny Rocco. Frank refuses and puts the gun down. But Sawyer grabs the gun and proves he is willing to take the shot... and finds the gun isn't loaded.
- Later, Frank comes to James Temple's defense, and Rocco gets angry enough he actually tries to shoot him. But nothing happens—by mistake, Rocco was holding the still-unloaded gun from before.
- Lady Drunk: Gaye, who spends most of her time in the hotel begging for liquor. It seems that being Rocco's moll hasn't been good for her.
- The Mafia: Rocco and his gang are old professionals from the heyday of the 1930s. One of them talks about the possibility of Prohibition coming back, which would return the gang to their former glory.
- Multiple Gunshot Death: Frank has to shoot Rocco, who is attempting all the while with his last strength to raise his gun and shoot Frank, three times before he finally stays down.
- The Place: Key Largo.
- Romancing the Widow: Frank with Nora, although it's mostly on her part. Frank is still dealing with the guilt of surviving the war where his friend - Nora's husband - hadn't.
- The UST in this film is unbelievable, just waiting for them to kiss. And they never do.
- Shout-Out: One that most viewers won't get. But Frank tells Nora about being with Nora's husband at the battle of San Pietro, and how her husband was killed and buried by the ruins of a church. Well, there really was a battle of San Pietro, complete with a bombed-out medieval church. It was the subject of Army documentary film The Battle of San Pietro, directed by—John Huston.
- Silent Whisper: Rocco's whispering to Bacall's character. We never know what was said, of course, but obviously it must have been horrible, and the viewer is basically free to set the perversion meter at just past their own tolerance level.
- The So-Called Coward: Frank appears cowardly in Rocco's eyes because the "living war hero" refuses to pick up a gun and take a shot at the mobster. Nora and James both believe that Frank could tell the gun wasn't loaded from the weight, but Frank rebuffs such talk. Frank's desire to "make a world in which there's no place for Johnny Rocco" comes back after the sheriff mistakenly kills the Osceola Brothers for the deputy's death and it looks as though Rocco will get away.
- Spiteful Spit: Nora spits Rocco in the face out of contempt.
- Suspiciously Apropos Music: Gaye sings "Moanin' Low," a song about a woman in an abusive relationship, which describes Gaye to a T.
- Would Hit a Girl: One of Rocco's henchmen gets rough with Gaye because of her drunkenness.
- You No Take Candle: The way the Indians speak (with proper American accent no less).