John Hammond's partner, George Sullivan, dies in an apparently accidental death, with Hammond the beneficiary of his double-indemnity insurance policy. Since this is the fourth double-indemnity death in the Sam Marlo, California vicinity in recent months, the company assigns investigator Tom Davison to the case. The partner's daughter, Nancy Sullivan, cooperates with Davison in the investigation, and Davison joins Hammond's business as a salesman. Davison is closing in on the gang, led by Chuck Malone, when the gamblers behind the racket kill Hammond, making it appear as a suicide to protect themselves. Davison gets conclusive evidence against the gang when they kill another man for his insurance, but the mob kidnaps Davison.