Artist Connor Simpson is shocked when a pig's heart is nailed to his cottage door. Connor is a member of Midsomer Worthy choir, with Joyce Barnaby, George Bullard, Carolyn Armitage, owner of the Hartsmede Estate, haulier Leo Clarke and Stephen Latimer - who used to sing for the rival choir in Aston Wherry. Conductor Laurence Barker, a perfectionist, is trying to prepare them for the Four Choirs competition.

At choir practice, Connor collapses but insists he is ok. But when Stephen visits later he finds him dead. Just then, a mystery woman rings Connor's phone. Barnaby and Jones find women's clothing, two used brandy glasses and the pig's heart. They question Stephen who admits he was once close to Carolyn.

Barnaby chases a shadowy figure outside church - it's Sam Judd, sacked estate manager at Hartsmede. He claims to be birdwatching. The next day, Joyce and the choir receive death threats but vow to continue. Stephen visits Carolyn, who missed practice, and ends up in a fight with her husband Giles.

Jones joins the choir while choirmaster Laurence angrily claims rival conductor Francis Crawford cheated his way into a prime job at the cathedral. His marriage to Ellen, a children's entertainer, seems tense.

Sam is taking photos at Hartsmede when a gunman fires. His body is found outside the estate walls, but when the police visit, Carolyn is sedated after a quad bike fall.

Connor's cottage is burgled. In the house is a tuning fork, like Laurence's. Carolyn turns up to choir practice in her night-clothes, looking deranged. Giles still won't let the police speak to her. But Kath Bullard, a GP, tells Barnaby that Carolyn has not been prescribed tranquilizers.

Ellen Barker admits making the call to Connor's phone. She was in love with him and Laurence raided his home to destroy evidence of the affair. The police find Crawford at the church, making secret recordings. He admits sending death threats.

Sam Judd's photos reveal secret meetings between Giles, Connor and Leo Clarke. As Barnaby and Jones go to Hartsmede, they find Giles pushing his wife into the lake.

Why is Giles drugging Carolyn and what is the connection between the three men? Can the police discover the truth about Connor's past and why he was killed - and will the Four Choirs competition go ahead?