Gay Lawrence, the debonair sleuth known as "The Falcon," and his sidekick Lefty arrive at dockside to meet a Latin American cruise ship carrying Gay's brother Tom. In Tom's cabin, homicide inspector Timothy Donovan of the homicide informs Gay that his brother is dead, a victim of suicide. After Diane Medford, a shipboard companion of Tom's, offers Gay her sympathy, the sleuth instructs Lefty to follow her in their car. As they tail Diane, Gay announces that the corpse on the cabin floor was not his brother, nor was he a suicide victim. Gay tracks Diane to a fashion show at her employer Madame Arlette's salon, where she is greeted by her fiancé, fashion editor Paul Harrington. Also at the fashion show are two other passengers from the boat, Latin American dancers Carmela and Valdez, who request one of Arlette's designs. Before Gay can approach Diane, he is stopped by eager reporter Marcia Brooks. Finally dodging the inquisitive reporter, Gay follows Diane to her office, but as he steps in to interrogate her, a gunshot rings out and she keels over, dead. Although Gay sees the murder weapon lying beside Diane's body, he runs into the alley, where he bumps into his brother Tom and informs him of the murder. Just then Inspector Donovan, who has been following Gay, arrives at the scene and arrests Lefty for the crime. While on the trail of Diane's murderer, Gay steps into the street and is run down by a speeding car. Tom takes his unconscious brother to his apartment, where he is greeted by Marcia, who demands information about the murder. Tom convinces her to return the next morning and the following day, Lefty, who has been released with a suspended sentence, arrives at Gay's apartment and learns that his boss will soon regain consciousness. Marcia then informs Tom that the murder weapon is missing, prompting Tom to return to Arlette's to investigate. At the salon, Tom makes a date to meet Arlette at a nightclub and there informs her that the police have found the murder weapon and are tracing the serial number. Arlette abruptly bids the detective good night, calling Donovan with Tom's whereabouts before she leaves the club. After eluding the inspector once again, Tom and Lefty search Arlette's salon, where they find the gun hidden in a mannequin. When Donovan tracks them down at the salon, Tom introduces himself as Gay's brother, and the inspector arrests him for false impersonation. After proving his identity, Tom is freed and directs Marcia to investigate Harrington's photographer, Savitski. Tom then visits Arlette and, after showing her the gun, forces her to admit that she hid the weapon to protect Harrington, with whom she is in love. Confronted by his gun, Harrington denies murdering Diane and is exonerated by a ballistics expert. Just as they reach a dead end, Marcia discovers that Savitski is an illegal alien. As he is questioned by Lefty and Tom, Savitski is about to reveal a clue when he falls dead, knocking a pile of magazines off his desk. After determining that Savitski was killed by a poisoned cigar, Tom hears a noise outside the office and instructs Lefty to pose as the photographer. At that moment, Valdez and Carmela enter the office to threaten Savitski at gunpoint. When Tom steps out of the shadows, the pair identify themselves as Mexican counter-espionage agents and explain that Diane was killed because she knew too much. After notifying Donovan of Savitski's murder, the agents and Tom and Lefty disperse, and Tom carries the magazines back to Gay's apartment. Certain that Harrington is involved in the murders, Tom and Lefty scrutinize the magazines for a clue when Marcia arrives and notices that a magazine cover dated 7 December, the day that Pearl Harbor was bombed, was shot in Honolulu. Realizing that the covers reveal information about planned sabotage, Tom deduces that the next incident is to take place that day at a New England inn. Tom and Marcia speed off to New England, and just after they leave, Gay regains consciousness and he and Lefty proceed to New England, also. Tom and Marica find the small Eastern town populated by German agents, and after Tom recognizes the ballistics expert as one of the agents, Harrington orders them imprisoned at the base of a bell tower. Discovering that the agents plan to shoot a Latin American envoy as his plane lands, Tom struggles to reach the rope attached to the bell's clapper. Just then Gay drives up and as he argues with the agents, Tom begins to ring the bell, drawing Gay's attention to a machine gun aimed at the diplomat. Gay steps in front of the diplomat just as the gun cracks, sacrificing his own life for that of an ally. With the spy ring smashed, Tom is about to leave town when he receives a threatening phone call from a foreign sounding voice and decides to stick around.