Christmas is coming and Barnaby and Jones are taking part in a team-building exercise organised by acting Chief Superintendent John Cotton, a young and ambitious officer. The weekend is run by Midsomer Yeomanry's TA, under the command of Colonel Matt Parkes, a haulage boss, Captain Tim Galsworthy, who runs a classic car business, and Sergeant Ed Lovell. The TA is also preparing for a war game in the woods.


Joyce is practising for a carol concert at Calham Manor Military Hospital, also the home of peace campaigner Caroline Halsey. Fellow choir member Penny Galsworthy is angry and still grieving for her daughter Gilly, who committed suicide two years earlier.


At Parkes yard, Matt's son James runs the business but he also seems to be involved in some shady activities with truck driver Dale Mitchinson. Later that night, as Dale's dad Don does his rounds as watchman and Penny hides in the shadows, there's an explosion.


Barnaby and Jones escape from Cotton to investigate the fire. Jones knows James from schooldays and the detectives also feel Don and Dale are hiding something. Forensics identify arson as the cause of explosion and the footprint of an Army boot is found near the scene. James points the finger of suspicion at Caroline - his grandmother.


Layla Barkham, the daughter of TA sergeant George and his disabled wife Nina, reveals that James got Gilly Galsworthy pregnant then dumped her. She hanged herself in Calham Woods. Layla also hates James for returning to Midsomer and taking the haulage company from her father, ruining her chances of going to medical school.


Barnaby discovers that Caroline has a conviction for causing explosions, while James and Tim sell a restored Lamborghini to a young, rich customer. Then a man's body is discovered in a trunk floating on the surface of Calham Lake. He is identified as Alec Grainger, the owner of a classic Bentley who was seen arguing with James.


James is arrested but claims the row was over his relationship with Grainger's daughter. But WPC Stephens discovers Grainger has business links to both Tim and James.


As Barnaby and Jones search for James, the TA begin their war games. There's a scream in the darkness and Layla, Caroline and Penny are found with the blood-soaked body of James. What shady business was he involved in - and who killed him and Grainger?