Stewart Moss and Lynn Loring are members of rival political families and are seeing each other. But if you are thinking this is a Romeo and Juliet story on Perry Mason nothing could be further from the truth.
Loring is the sister of candidate Richard Anderson who is running for State Senate against Ford Rainey the incumbent. Moss is his stepson and he's a wild child. Even without the political rivalry there's plenty of reasons that Anderson shouldn't like him messing with his sister. For one thing he's just written a bad check to cover gambling debts so he's got people in Las Vegas interested in him. It's Moss that winds up shot to dead, but neither Anderson or Loring are arrested.
Instead it's Jan Shepard who is Anderson's wife who discovers the body and takes the murder weapon because she concludes it was her husband or sister -in-law that did the deed. She's the one needing Raymond Burr's help.
It is gambling at the root of the murder, but that's all the hint you get from me. Moss was about to upset a lot of finely conceived plans and someone didn't want that. It's one pathetic confession the murderer makes on the stand.
This one is a good story and you probably won't guess the murderer. And that's the test of a good Perry Mason episode.