Ernie Mott is a restless, irresponsible, wandering Cockney with a good musical ear. On Armistice Day, Ernie visits the tomb of the Unknown Warrior in Westminster Abbey, which memorializes those who died in World War I, including his father. Ernie wants a better life but does not want to settle down or work for it. When he returns home, his mother Ma asks why he has returned after so long, and she gives him an ultimatum that he must stay home now or leave forever. He informs her that he will then be leaving next morning, and goes out to get a drink. He meets fellow musician Aggie Hunter outside the bar, but instead prefers the company of a gangster's fickle former wife, Ada Brantline. However, when Ernie becomes smitten with Ada she rejects his offer of a date when he tells her he will be leaving town the next day.
The next morning, Ma tells her pawnbroker friend, Ike Weber, that she has cancer. Ma and Ernie get into another fight, but after he storms out, Ike shares with him that his mother needs him in her battle with cancer. Ernie returns and says that he will stay with her at home and help her run her shop.
A month passes, and Ernie continues to pursue Ada. However, when gangster Jim Mordinoy informs him that she is still his wife, Ernie does not believe Ada when she says that is a lie and he cuts her off socially. Ernie begins to notice the poverty surrounding him in London, and chooses to accept Mordinoy's offer to join his activities, even against Ada's pleas. Ernie begins to steal cars, and he is involved in a police chase until his car collides with a truck and explodes into flames. Ada implores him to run away with her, but he does not want to leave his dying mother.
When Ernie is eventually bailed out of jail by Ike, he finds out that after the police discovered Ernie's platinum cigarette case — his birthday gift from Ma — was stolen, the police arrested Ma and put her in prison. She begs for forgiveness for shaming the family, and dies in prison hospital. When he returns home, he learns via a letter from Ada that she decided to stay with Mordinoy because that would make her life easier. Ernie is crushed, and walks along the street until he gets to Aggie's door and walks in.
