The Narrow Margin

Detective Brown and Sergeant Forbes are assigned to protect Frankie Neall, a mob boss's widow, as she travels from Chicago to Los Angeles to testify before a grand jury. They accompany her as they leave her apartment, aware the mob will try to intercept the payoff list. The mission starts under a cloud of danger.

As they leave the apartment, mob assassin Densel ambushes the group. Forbes is shot to death, and Densel escapes, possibly wounded by Brown. Brown survives but realizes the danger has only begun.

At the train station, conductor Joseph Kemp enters Brown's compartment under the pretense of finding lost luggage. The encounter marks the start of a tense cat-and-mouse game aboard the train. Brown remains wary of Kemp's true intentions.

Kemp searches the compartments but finds nothing suspicious. Brown moves to the dining car to mislead him, hoping to keep Neall safe and unobserved. The search delays the mob's plan while the danger tightens on the train.

Mobster Vincent Yost attempts to bribe Brown to reveal Neall's location and abandon her. Brown refuses and warns him he is acting under arrest for bribery, but Yost dismisses the claim and implies Brown's doubts about jurisdiction. The encounter underscores the moral peril Brown faces on the rails.

Brown befriends passenger Ann Sinclair and her young son Tommy, becoming a protective ally. Kemp spots Brown with Ann and concludes she is Neall, adding a layer of mistaken identity to the journey. The companionship also places Ann in the crosshairs of the mob.

After a confrontation, Brown beats Kemp and takes him to a railroad agent, then hurries to warn Ann about the danger. The mob's plan hinges on misidentifying Neall, creating tension as the truth looms closer. The danger escalates with each stop.

During a stop at La Junta, Colorado, Densel boards the train and waylays Jennings, freeing Kemp. The mob's pursuit intensifies as the train continues toward Los Angeles. Brown remains on edge, knowing the payoff list is at stake.

Ann reveals she is the real widow, while the undercover Chicago policewoman Sarah Meggs acts as a decoy and test of Brown's devotion. The plot twist reframes who Brown has been protecting and why the mob remains so determined. The payoff list has already been mailed to the Los Angeles District Attorney.

As Brown and Jennings try to intervene, Densel shoots the decoy in the adjoining compartment after a struggle over the fake Neall. The violent turn raises the stakes and confirms the mob's ruthless resolve. Kemp resumes coordination with accomplices in a trailing car.

Brown uses a window reflection from the train to gain a clear shot and fires through the door, killing Densel. Kemp jumps off the train to reach the mob's trailing car, but the would-be conspirators are quickly arrested. The immediate threat on the train is neutralized.

The train arrives in Los Angeles and Brown escorts Ann toward an awaiting police car. Ann chooses to walk the two blocks straight to the grand jury, symbolizing a stand against intimidation. The two make their way toward the courthouse arm in arm.

The payoff list has been mailed to the Los Angeles District Attorney, ensuring the mob cannot use it to extort or silence witnesses. With the threat receding, Brown's protection mission concludes with the case moving forward. The mob's intercept attempt ends in defeat as the law closes in.