Trevor Radford, who manages a family brewery, dies after being hit on the head and dumped in a vat of beer. Trevor's brother, Stephen Radford, suggests that Trevor was cooking the books. Then Trevor's widow, Helen, goes to the brewery to look for Stephen (with whom she was having an affair) and finds him also murdered. Stephen's widow, Thelma, tells Morse he was a serial womanizer.
While this is all going on, a rival brewery, Farmer's, has made an offer to buy Radford's. The shareholders are not much impressed by the price offered, but they are divided. Charles and Isobel Radford, the dead brothers' mother and father, don't know what to do.
The main suspects are two Radford Brewery executives, Victor Preece and Norman Weeks. Both aspire to be managing director and both are chasing a secretary. But Morse looks around for other motives.
Then there is a third killing, when a local lawyer is beaten to death. Morse becomes convinced that everyone in sight is hiding things from him, including a surveyor to whom Trevor addressed a post-dated letter, which someone had tried to burn. To solve the case, Morse has to crack a wall of deception.