Montgomery is Kent, a callow rich boy who is sent to prison on a ten-year manslaughter sentence after killing someone while driving drunk. His cellmates are Morgan (Morris), who is doing a stretch for robbery, and Butch (Beery), a jovial, avuncular fellow who happens to be a multiple murderer serving a life sentence. Morgan offers himself as sort of a mentor for young Kent in prison, but Kent rejects Morgan's help, eventually becoming a cowardly stool pigeon. Meanwhile Butch, who has nothing to lose, is plotting a jailbreak.
The Big House is the Ur-Example of that sub-genre of film known as "prison flicks". In fact, although prisons were used as settings at least as far back as the 19th century and works like The Count of Monte Cristo, this may be the Ur Example period for works set in prison that explore prison life. It was a Star-Making Role for both Beery and Montgomery. Beery had been unemployed when MGM hired him for this film, his contract with Paramount having expired.note Beery got an Academy Award nomination for Best Actor and was a leading man for most of The '30s.
- Affably Evil: Butch sure is awfully cheerful and affable for a person who has committed who knows how many murders.Butch: Sadie was a good old skirt. I shouldn't have slipped her that rat poison.
- Day Hurts Dark-Adjusted Eyes: Butch is squinting after his time in the dungeon.
- Dirty Coward: Kent becomes this. When the guards arrive for a routine frisking, Kent slips Butch's knife into Morgan's coat. Morgan, who was going to be released on parole the next day, has his parole revoked.
- Earn Your Happy Ending: After having lost out on his parole thanks to Kent, having escaped only to be recaptured, and having been shot in Butch's breakout attempt, Morgan gets a Happy Ending. His heroism in saving the lives of the guards wins him a pardon and a happy life with Kent's sister Anne (Leila Hyams).
- Even Bad Men Love Their Mamas: Butch, the multiple murderer and hardened convict, breaks down and weeps upon being notified that his mother has died. This is the motivation for his escape.
- Foreshadowing: The warden says to Kent, "And remember, this prison does not give a man a yellow streak, but if he has one, it brings it out." This is exactly what happens, as Kent becomes a cowardly stool pigeon.
- Getting Crap Past the Radar: The prisoners receive magazines. One, called "Bride's Confession", has been "worn out"—clear references to pornography and masturbation which were not explicitly allowed even in The Pre-Code Era.
- Go Mad from the Isolation: One of the prisoners has cracked. He thinks that the bug-filled fish slop served for dinner is steak with mushrooms.
- Great Escape: Morgan successfully escapes from the prison by sneaking into the morgue and being carted out as a corpse. Later, Butch's mass breakout is foiled by Kent's betrayal, turning into a long, bloody shootout.
- Hostage Situation: After the breakout has gone bad and the prisoners are barricaded in the cell block, Butch forgets about the "affable" part of Affably Evil, executing the guards one at a time as he demands transport out of jail. Morgan short-circuits this plan by locking the rest of the guards away.
- Idiot Ball: The warden. Informed by Kent of Butch's mass breakout plan, he allows the breakout to happen, with his only action being to station machine-gunners outside the front gate. This is the reason for the epic bloodbath riot that is the climax of the film.
- Institutional Apparel: Drab gray (probably) outfits, rather than the more stereotypical striped prison uniforms. Kent's receiving of his Institutional Apparel shows how he's being absorbed by the system.
- Laser-Guided Karma: Kent, the coward and stool pigeon who betrayed the breakout to the warden, is shot down in the chaos of the battle.
- Match Cut: A pretty interesting audio Match Cut between the prisoners banging their cups on the table, demanding better food, to the rattling of machine guns as the guards fire warning shots.
- Never Learned to Read: Butch gets a letter, and weaves a fanciful story to the other inmates of how some girl wrote him a sex letter ("The rest of this is too juicy for you guys!"). He's making it all up, as he can't read. When they're alone, he gives Morgan the letter to read to him.
- Officer O'Hara: Prison Guard O'Hara, in the case of Pop Riker and his thick Irish brogue. Riker says that it's a mistake to put a weakling like Kent in with a hardened criminal like Butch, but the put-upon warden notes ruefully that thanks to prison overcrowding, they don't have a choice.
- Prison: Yep. The movie is a "message film" of sorts, based around the theme of how dehumanizing life in prison is, and how the public appetite for cramming people into prisons without providing any means for their rehabilitation only breeds more crime.
- Punishment Box: "The dungeon", the prison's solitary confinement ward. One of the most memorable scenes in the movie occurs after Morgan and Butch both get sent to the dungeon. The camera remains stationary, outside an empty hallway, showing a line of closed doors. The prisoners then talk to each other from inside their cells.
- Seven Minute Lull: Butch and the gang, planning the Great Escape, are passing some guns and ammunition to each other while intoning the Lord's Prayer in the prison chapel. As the prayer comes to an end, one of them accidentally drops a bullet on the stone floor, causing them all to tense up.
- So Much for Stealth: See Seven Minute Lull above.
- The Stool Pigeon: Kent is seduced by a prison stoolie, and becomes one of these, a particularly cowardly one who informs on his friends. In the end, he betrays Butch's plan for a breakout, resulting in the bloodbath that closes the film.
- Welcome Episode: The whole opening sequence of the movie involves Kent arriving at prison, being processed and issued prison clothes, and arriving in his cell. This establishes the setting, mood, and characters.
- You Are Number 6: "From now on, you'll be number 48642", says a guard to Kent. Subverted in that despite that scene, the prisoners are always referred to by their names.