In Southern California, Perry Mason defends Barry Davis against charges that he killed his former boss, Mort Lynch. Barry is a mixed-up young man and he and Lynch had recently argued resulting in young Barry quitting his job. Barry's uncle had been an associate of Lynch long ago. Lynch was also running for Mayor and trying to shake up the local power structure in the town, controlled by Dell Harper who runs the local newspaper. Barry is hired by Dell to dig up dirt on Mort Lynch and specifically how he got the money to start in business in the first place. Barry learned from having hired Paul Drake to look into his uncle's background, that he was quite a crook. Barry then learned from the local insurance agent that Lynch received $40,000 from a life insurance policy on his uncle. Barry finds a plate for printing $10 bills in a tool case Lynch has. An old counterfeit 1940 $10 bill found on Lynch is the clue that points to blackmail and a motive for murder.
—garykmcd