Debbie Moffett is crushed to death by a giant round of cheese just hours after an argument at a Parents’ Council meeting at Midsomer Pastures Prep School. Debbie worked at the dairy which produces the world-famous Midsomer Blue and was found by her colleague Jim Caxton. Jim seems more anxious about his precious cheese than the death of Debbie.
Barnaby and Jones break the news to Debbie’s daughter Holly and headmistress Sylvia Mountford. Former England rugby player turned dairy owner Gregory Brantner comes home from a night at a hotel. Gregory’s wife Hayley, Oliver Ordish’s wife Beatrix and Jim’s sister-in-law Helen were all at prep school together and the Brantners recently returned to Midsomer to take over Hayley’s family business.
Detectives are suspicious when no-one has a bad word to say about Debbie. Then Kate discovers Holly was being expelled. She’s on a dairy scholarship which carries strict rules – which Debbie was breaking by allegedly having an affair. Debbie’s phone leads police to Oliver, who works for the cheese board. He admits they were sleeping together.
Gregory explains that Debbie was helping him with his business – despite winning awards, its cheese-making is labour-intensive and loss-making. Just then, Helen arrives and empties her milk delivery over the yard, angry that Gregory has cancelled her order.
Beatrix and Oliver argue and he storms off. When he returns from the pub, he is garrotted and the next morning Kate finds his mouth full of unusual maggots.
The dairy appears to be crucial to the case. Helen’s husband killed himself because his farm was struggling and Jim suspects she may be taking revenge. Then Beatrix’s daughter Poppy disappears. Gregory admits he was due to meet Debbie the night she died to celebrate a new controversial deal, making Midsomer Blue for a national supermarket chain. Meanwhile, as Hayley tries to comfort Beatrix, Jones finds her missing daughter.
Jim is sacked as Kate suspects Oliver was killed with cheese wire and covered with cheese fly larvae and Jones discovers Gregory was paying the dead man a consultancy fee. Gregory tries to reassure Hayley that the dairy has a future, but that night he goes to investigate an alarm at the dairy and is stabbed through the heart with a cheese needle. Hayley tries to talk to Helen but her old school friend is not interested.
Then Jones discovers Beatrix had a child as a teenager – Jake, now an animal rights activist. Helen is hit with a wrench as she tends her cattle. Jim finds her and they declare their love before being trampled to death. Nearby, Jim’s car is full of maggot-laden cheese.
Sylvia tells Beatrix and Hayley things have got out of hand. They deny any involvement but on the way home Beatrix collapses. Help comes from an unexpected source and the police rush back to their school. Can they stop the killer before the bitterness of the past leads to yet more deaths?