Kent Taylor as Detective Lieutenant Bill Bannister, assigned to run down the terrorist gang, is given a double motive when mobsters shoot and kill his brother after "Leagues" wily leader has slipped through a police trap. Pursuing his brother's killers, Bannister attempts to arrest one of them, Tabont, but while they struggle in a plane the pilot is shot and the aircraft plummets madly earthward.
Kent Taylor as Detective Lieutenant Bill Bannister, assigned to run down the terrorist gang, is given a double motive when mobsters shoot and kill his brother after "Leagues" wily leader has slipped through a police trap. Pursuing his brother's killers, Bannister attempts to arrest one of them, Tabont, but while they struggle in a plane the pilot is shot and the aircraft plummets madly earthward.
Pursuing baffling clues involving the "League of Murdered Men," Detecitive Bannister narrowly averts death in a plane, only to get into a series of scrapes with the terrorist gang. Racing in a new machine he averts a head-on collision with a mob car by sending his own crashing down the well of a skyscraper garage.
Groggy from his headlong plunge from the death car in the nick of time, Bannister resumes his pursuit of professor Mortis' mob. As he and Tim close in on the killers, one of them kidnaps Vicki and, with her as a shield, makes his getaway in a car. Hotly pursuing, Bannister sees the car with Vicki clinging to the running board, plunge through the guard rail of a high over-pass.
Sensing that Bannister, is a tenacious threat to his terrorist plots, the professor sets a trap for the detective. His scheme is to capture and bring him to the gang's hideout where, through the use of drugs, he will be inducted into the mob. To this end, he decoys Bannister to an isolated warehouse where several members of the gang lie in wait to capture him alive.
Escaping from the warehouse trap with the timely aid of Tim, Bannister uncovers a mystifying new clue to the mob's activity, which leads him to a waterfront dive. There he is surprised by members of the Professor's gang and engages them in a roof-top struggle in which he is overpowered and forced over the parapet.
Falling from the roof, Bannister escapes death when his drop is broken by an awning. While evidence now clearly indicates that the Professor's mob is made up of men listed officially dead, the detective faces the baffling task of preventing the dynamiting of city hall. As the zero-hour approaches, he frantically searches the doomed building for Vicki.
BILL Bannister and Vickie miraculously escape from the blast-shattered building to find that the professor has pulled a coup in looting a downtown bank during the confusion. Close on the heels of the mob, Bannister and Tim Nolan trail them to a waterfront dive and are closing in for the arrest when Bill plunges out of sight through a secret door and disappears.
Bannister is rescued from a water-filled dungeon in Frenchy's but succeeds, with the help of Tim, Vicki and Happy, in driving off the gang and getting the bank loot. Meanwhile the Professor "Plant" a pistol in a camera which Vicki takes on a new chase of the mob. Seizing an opportunity to get a candid shot of Bannister, she focuses it on him and presses the shutter-re-lease. It explodes.
Detective Lieutenant Bannister escapes Vicki's lethal camera shot and balks an attempt by the Professor's mob to make off with an armored payroll truck after a hot gun battle. Certain that there is a traitor among those working close to him, Bannister lays a trap with the collusion of Chief O'Brien. Meanwhile, however, he is stripped of his badge and office and is given a further setback when the payroll money is lifted mysteriously. On the heels of this, Bannister is attacked by the mob, and unconscious, is shunted into the traffic lanes in a driverless auto.
Bannister is saved from death in racing traffic by Vicki. While traitorous suspicions point to the reporter, Happy Haskins, as having an alliance with the Professor, the detective follows a tenuous trail to a dynamite plot which has police headquarters as its daring objective. Foiled momentarily, Bannister wins a dubious advantage when he gains the wheel of a dynamite-ladden truck which threatens to explode at any moment.