Private Detective Michael, in pre-war America, in compliance with the wishes of his girlfriend, Merle Garland, takes a job at an airplane factory, and immediately the diamonds used for special instruments are stolen in what Shayn suspects is an inside job. THe trail leads him to a dress manufacturer who is a Nazi agent, smuggling diamonds to Hawaii as dress buttons. On the boat to Hawaii, Shayne finds that an old friend, Helen Shaw, is working with the smugglers. After he and a federal agent, Juan Arturo O'Hara, quit chasing each other and, alter trapped by the gang, the case is solved and the smugglers brought to justice.