Wealthy horse breeder and trainer Graham McVeigh is exasperated by his younger brother Teddy's compulsive gambling, and is tired of bailing him out of debt and scrapes with the mob, so he decides to rid himself of the problem. He convinces Teddy to bet heavily on one of his (Graham's) horses, then drugs the horse so that it loses the race, costing Teddy thousands and sinking his chances of winning enough money to pay off mob bookie Bruno Romano. Graham tells Teddy that he has arranged a meeting with Romano in a secluded spot, where they can work out their differences. However it is a trick to lure Teddy out into the woods, where Graham shoots him once in the back of the head to make it look like a mob execution. Later, he phones Romano to tell him that he wants to pay off Teddy's debts, and lures Romano over to his ranch, where he shoots him too, claiming self-defence when Romano pulled a gun on him.
However, Graham did not reckon on Romano's boss, Vincenzo Fortelli, taking exception to Romano's death (and the loss of Teddy's gambling debts), and soon finds himself threatened by both Columbo and Fortelli. Columbo forges an unlikely partnership with Fortelli (hence the episode's title) in an attempt to trap McVeigh into confessing the murders.