Just when Frank Smith has some vacation time planned, a call to help police in San Diego comes in. Diamond thieves have been looting safes at hotels at gun point. Joe Friday gives the details in voiceover to bring us up to speed on the criminal activity as he and Frank go to San Diego to assist the police there.
The concern is that the goods are being taken South of the border and sold through a fence. Suspects are identified, and an initial raid on their apartment turns up scrapbooks of news stories of the robberies. Stakeouts are set in place, while the criminals are interrogated. Will the hard cases crack? Can Joe Friday find something to drive a wedge between the loyalties of the gang of thieves?
The stolen jewels are yet to be found, and Joe Friday goes undercover to infiltrate the ring of bandits. It'll be tough, but can he get back the jewels before the collection is broken up and sold? One by one, the gang members are hauled off to jail, and it's only a matter of time before the ringleader is zeroed in on and picked up.