In the turbulent Dublin of 1922, we meet Gypo Nolan, an outcast from the Irish Republican Army (IRA), who was expelled for failing to take the life of a Black and Tan responsible for the murder of a fellow IRA member. Driven by anger, Gypo witnesses his streetwalker girlfriend, Katie Madden, struggling to fend off a potential customer. Unable to contain himself, he aggressively tosses the man into the street. Katie, in her despondency, reveals her need for £10 to escape to America and begin a new life.
Amidst this turmoil, Gypo encounters his friend Frankie McPhillip—a fugitive marked with a £20 bounty on his head. Tired of a life on the run, Frankie yearns to see his mother and sister, Mary. Under the cover of night, Gypo naively decides to betray Frankie in exchange for the reward that would allow them both passage to America. Tragically, the British forces track Frankie to his home, leading to a violent confrontation that costs Frankie his life. As a cruel twist of fate, Gypo receives his blood money from the British and walks free.
In a desperate bid to fabricate a convincing story, Gypo buys a bottle of whiskey and lies to Katie about acquiring the money by roughing up an American sailor. At Frankie's wake, his behavior raises suspicions when coins spill from his pockets. Although the men around him dismiss the notion of him being an informer, Gypo's conscience begins to plague him as he moves to deflect blame onto a man named Mulligan. However, words spoken in his intoxicated state lead others to question his innocence.
Meanwhile, Mary reports that the only person Frankie conversed with before his demise was Gypo, prompting the IRA to launch an investigation into the murder. Gypo, desperate to locate Katie, stumbles into an upper-class gathering where his drunken antics spiral out of control. His former comrades soon apprehend him, taking him to a makeshift tribunal, where Mulligan is interrogated. The group, however, chooses not to believe Gypo's accusations, providing a detailed account of how he spent the £20. Ultimately, Gypo's guilt compels him to confess his treachery.
Secure in a cell yet fearing for his life, Gypo seizes an opportunity to escape through a ceiling hole and rushes to Katie's apartment, where he confesses his betrayal. Despite her fervent pleas to Commissioner Dan Gallagher, he coldly refuses to spare Gypo, citing the risk of him turning the entire organization over to the police. Meanwhile, other IRA members, upon overhearing Katie, converge on her apartment and fatally shoot Gypo, leaving Katie devastated as she hears the gunfire.
In his final moments, Gypo seeks refuge in a church where he encounters Frankie's mourning mother. He implores her for forgiveness, and she graciously absolves him, stating he acted without understanding the consequences of his actions. In a poignant moment of redemption, Gypo passes away content, calling out joyfully to Frankie as he lies on the church floor, embraced by a sense of peace.
