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
CinemaSerf
On the trail of some industrial diamonds that go missing from the safe of his new employers, loved-up but down on his luck detective "Mike Shayne" (Lloyd Nolan) begs and borrows some cash so he can travel on an ocean liner upon which he is sure are the thieves. Pretty soon the presence of "Helen" (H...