From The Perry Mason TV Show Book (Revised)
This is another of the handful of episodes in which Perry doesn’t appear. Mike Connors, who went on to star in his own successful series, Mannix, plays Joe Kelly, a lawyer friend of Paul Drake.

Perry is in Europe on business. Paul and Joe Kelly are vacationing in Tesoro, a small town run by Bonnie Mae Wilmot, a woman known by the locals as the duchess. Bill Jaris, who was married to the duchess’s late daughter, and his brother run a bowling alley that the duchess wants closed. An outbreak of dysentery linked to the bowling alley results in an injunction to close the place, to the delight of the duchess.

Paul is a friend of Bill’s, so he and Joe help get the injunction quashed for the time being. But Bill is soon in more trouble: Dr. Max Taylor, a man working with the duchess to close down Bill and his brother, is murdered. Bill is the number one suspect. Now Joe must work to free Bill.

It was his work in this episode that led the Mason series producers to consider Mike Connors as a replacement for Raymond Burr after he threatened not to re-sign his contract.