Allen Grey, a young G-man, is in love with Sondra Washington, whose brother Douglas, a nightclub owner and boxing promoter, is suspected of stealing firearms from government warehouses and selling them to mobsters. Although Grey and his confederates have been assigned to gather evidence against Washington and his gang, Sondra believes her brother to be an honest businessman and feels that Grey is misguided. In order to gain access to Washington's inner circle, Grey trains as a pugilist and works his way up through the ranks of prizefighters, eventually attracting the attention of Washington, who gives him a job as a truck driver. While gathering evidence, Grey stays in touch with his superiors via a shortwave radio installed in the truck's cab. The G-men end up pursuing Washington's gang in an automobile chase and win the final shootout.