Childhood chums Rocky Sullivan (James Cagney) and Jerry Connelly (Pat O'Brien) grow up on opposite sides of the fence: Rocky matures into a prominent gangster, while Jerry becomes a priest, tending to the needs of his old tenement neighborhood.
Rocky becomes a hero to a gang of teenaged boys (played by Dead End Kids Billy Halop, Leo Gorcey, Huntz Hall, Gabriel Dell, Bobby Jordan and Bernard Punsley). Father Jerry despairs at this, asking Rocky to lay off so he can keep the kids on the straight and narrow.
Then Rocky's crooked business associates George Bancroft and Humphrey Bogart attempt to end Father Jerry's radio campaign against the rackets by killing the priest. Rocky (whose cynical outlook on life has been softened by his romance with true-blue Anne Sheridan) shoots them down and takes it on the lam.
Arrested and convicted of murder, Rocky sits smugly on death row, fully intending to go to the chair with a smile on his face. A few moments before the execution, Father Jerry pleads with Rocky to turn yellow so that the tenement kids will despise his memory.