Graham McVeigh has had it with his ne'er-do-well brother Teddy, who is a degenerate gambler and is in serious debt to his bookie, Bruno Romano. He develops an elaborate plan to eliminate both of them, by first having Teddy suffer a large loss at the track - Graham drugs his own horse, a sure winner, so it loses - and then framing Bruno for Teddy's murder. He then arranges for Bruno to come to his house, ostensibly to collect Teddy's losses. He then kills Bruno and claims self defense. Lt. Colombo begins to find a number of anomalies that he simply cannot explain, including mice in a restaurant bathroom. He's pretty certain Graham is responsible for both murders, but he will need some assistance in order to get a confession out of him.
—garykmcd