From The Perry Mason TV Show Book
Someone actually puts one over on Perry in this episode. When wealthy art connoisseur Otto Olney throws a party to celebrate his purchasing a rare painting by Gauguin, he is furious when a party guest named Durant says that the painting is actually a fake.

Perry comes up with a plan to have Olney sue Durant for libel. But here's where Perry’s been had. Durant claims he never said anything about the painting and the only witness, a woman named Maxine, agrees.* When Perry tries to get in touch with her, he learns she’s left for an art school and won’t testify. Since he can’t catch up with her, he tries her apartment for a clue and finds the dead body of Colin Durant, fully clothed, in Maxine’s shower. The police get to Maxine when Paul does and arrest her for the murder of Colin Durant. Perry takes the case and is thrust into the world of art collectors and art forgers.

* Webmaster’s Note: Joel Peebles notes that Maxine did not agree. In fact, she gave Mason an affidavit stating that Durant did tell her that the Gauguin was a forgery.