In Washington, D.C., Bruce Cabot plays Frank Marshall, and Crawford Weaver plays Slim Hewitt, two postal inspectors freshly sworn in to protect the nation’s mail system. A bomb, mailed from the fictional town of Stanfield, Connecticut and addressed to U.S. Senator Morton, is discovered in the Senate mailroom, and the two men are dispatched to Stanfield to get to the bottom of the threat. On the train, Frank meets Nancy Foster, Marguerite Churchill, a resident of Stanfield, and a cautious rapport begins to form between them.
Upon arrival, they slip into Stanfield under assumed names and secure jobs in a local factory. Dinner with Nancy at her home reveals a troubling truth: the Hood Legion—a ruthless, fascist-tinged group that wields power with intimidation—has complete control over the town. The sense of danger intensifies as Frank and Slim realize that the factory, the newspaper, and almost every public sphere are under the Legion’s thumb.
To infiltrate the organization, the two men undergo a perilous initiation. In a dim room filled with masked members in long robes, they are blindfolded and pointedly faced with threats as guns are pressed to their heads, then given bullets as tokens of belonging. The initiation is brutal and convincing, signaling their acceptance into a group that uses fear to coerce loyalty.
Don Foster, Ward Bond, Nancy’s brother, grows anxious as he pleads with Colonel McCollum, Charles C. Wilson—the town’s powerful newspaper editor—to print Don’s accusations about the Legion. But the Legion moves quickly: Don is framed and arrested for drunk driving, though he is eventually released, only to be ostracized by the townsfolk. McCollum orders Don taken to the Legion’s secret tribunal in the woods, where he is found guilty and shot to death, a brutal display meant to stifle dissent and silence witnesses.
Nancy tries to seek help from the police, but the authorities are hampered by fear and inaction, unable to locate the killers. When Frank consoles Nancy, she compels him to confess his membership in the Legion, and she swears never to speak to him again. Undeterred, Nancy goes to the newspaper’s owner with her story, provoking a harsh rebuke of McCollum and prompting a grim decision: Nancy herself should face the Legion’s tribunal.
Slim confronts McCollum with the truth about Don’s death, and the editor sees Slim as a traitor to the Legion. Frank learns that Nancy and Slim are being held prisoner, and he secures the Governor’s intervention to mobilize the National Guard. In a dramatic rescue, the National Guard frees Nancy and Slim and arrests the Legion’s members, exposing the network of fear that has held Stanfield in its grip. The Legion’s true leader, McCollum, is revealed amid a tense escape attempt that ends in a fatal fire when his car overturns with him inside.
With the danger partially neutralized, Frank reveals his true identity to Nancy, and the two begin plans to marry. Back in Washington, the Post Office Department’s chief inspector offers formal congratulations for the successful sting operation, but issues a pointed warning: Americans are a nation of “joiners,” and this very trait makes them vulnerable to movements like the Ku Klux Klan and the Hooded Legion. These groups present themselves as patriotic and protective, yet they are often fronts for racketeers who exploit loyalty for their own gain. The film leaves viewers with a sober reflection on how easy it is for zeal and patriotism to be diverted into coercive power, and how vigilance remains essential to preserve democratic rights.
