This is punchy social realism about conditions in American prisons. James Cagney plays a crime busting news reporter who is framed for manslaughter after threatening to expose a corrupt DA running for Governor. Sent down for 20 years, he becomes socialised by the violence and demoralising monotony of his environment until he he is locked away in solitary.
It's a liberal Warners' protest story that crusades against a penitentiary system which entrenches its inmates' antisocial weaknesses. The wardens are a brutal, reflexly vindictive gang enforcing ceremonial rules. Cagney enters the pen as a law abiding citizen but is transformed into an unstable nucleus of vengeful fury who sides with the cons. And it's a potent performance.
The innocent man gets attached to a hardcore gangster (George Raft) who busts out and pledges to clear the reporter's name on the outside. He then goes back inside (!) to coerce a confession out of the convict who set up the frame. This part of the film doesn't work as well, mainly because it is hard to believe a tough mobster would stick his neck out so far for a cell buddy, and it's too sentimental.
There are the usual signifiers of a '30s prison film: Cagney has a girl on the outside who never stops fighting, and a heartbroken Ma; the meanest bull gets his just reward at the hands of a con he pushes too far; there's a desperate breakout that ends in a wall of bullets from the national guard. The reporter is reprieved and the prison boss turns out to be a liberal reformer! But this is what the censors demanded.