Daphne goes to visit her horse, Par-a-kee, at the stable the night before a race. She interrupts a man trying to inject the horse with a fatal virus. Daphne's father hires Dave to investigate, while a bookie begins spreading rumors about the Dutton stable to have Par-a-kee disqualified.

A theatrical producer's wife receives a note implicating her husband as a killer. He intercepts a second note and asks Ken and Sandy to find who sent the message. A man the producer hated, a former love rival, turns up dead, and there are no shortage of suspects.