 Using inside information obtained from Pete Madison, Jack and Sally Baron plan to steal $300,000 worth of gems from three traveling jewelry salesmen. Dan Mathews and Sergeant Williams are called when the first salesman dies from injuries sustained during the robbery. Information from diamond merchant Henry LeFaubre helps them narrow the focus of their search, especially after the thieves  second robbery yields only worthless sample diamonds. When Dan and Sergeant Williams find the discarded sample diamonds, they disable Jack and Sally Baron s car (which is parked nearby). After the stranded Barons are captured, Dan finds himself engaged in a high-speed chase involving the now-desperate Pete Madison