It's episodes like this one that show how "Diagnosis Murder" could be more than a weekly "whodunit." Not only do you have a taut script with tension and surprises, but you have award-worthy performances from two old pros who make it all look easy...Dick Van Dyke and Jack Klugman. Mark Sloan is at his determined best here, especially when given a case that ties to his past. But the real star here is Klugman. Fighting back a raspy voice brought on by cancer, he is genuinely moving as the cop on the way out the door with one last case to close. His actions to get his man are almost as interesting as the hunt for the killer itself.
The theme of the "Clown Killer" is particularly chilling. The first glimpse of the victim in face paint is jarring and it's a haunting image that hangs over the episode.
There's so much in this episode...questions of right vs. wrong; Harry's actions; the Mark/Trumble relationship. And it gives the series one of its coldest villains and most downbeat endings.
Lee Goldberg and William Rabkin's style fit this show like a glove. Dick Van Dyke and company knock this one out of the park, and a classic performance by Jack Klugman make this one of the best the show had to offer.