The Cisco Kid is captured while keeping a rendezvous with cantina dancer Dolores but is released by his captor, the commander of a U.S. Army regiment, to help break up a kidnap ring. On his way to Las Tables with his pal, Gordito, he makes a stop at the Martinez Rancho, where they learn that his friend Carlos has been kidnapped, from his wife Marquerita. At the Crystal Palace Saloon, Cisco runs into an old girlfriend, Sally, who he once jilted for a tight-rope walker, but she doesn't betray him when the sheriff and an army officer enter searching for Cisco.

Lloyd Nolan is back as detective Michael Shayne who's in search of a stolen coin.

Rival reporters compete to sign the Wyatt Quintuplets to be guests on their radio shows.

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.

In Puerto Rico to investigate a glut of contraband diamonds that are flooding the world's jewel market, Mr. Moto and his sidekick, a wrestler, find themselves involved in murders by thrown daggers, the frame-up of an overstressed Army colonel, and a pirate gang led by an unknown boss who has inside knowledge of the ensuing investigation.