In order to win back his girlfriend, Mike Shayne promises to give up his detective practice and get a job as riveter in an aircraft plant. He quickly finds himself investigating the theft of industrial diamonds from the plant's safe and, utilizing a variety of false identities, traces them first to a dress factory and later to a Hawaii-bound ocean liner. Escaping several attempts on his life, he is able to uncover a Nazi smuggling ring, but the location of the missing diamonds continues to elude him.
Lloyd Nolan
as Michael Shayne
Mary Beth Hughes
as Merle Garland
George Reeves
as Juan Arturo O'Hara
Helene Reynolds
as Helen Shaw
Steven Geray
as Vanderhoefen
Henry Victor
as Rudolf Hagerman
Curt Bois
as Friedrich Gerber, alias Nappy Dubois
Marie Blake
as Ethel
Emmett Vogan
as Charlie
Mae Marsh
as Mrs. Bertha Toby
Frank Orth
as Mr. Toby
Ivan Lebedeff
as Alexis Fournier
