Rent Midsomer Murders: Series 10: Death in a Chocolate Box (2007)

Attending a farewell presentation for ex-criminal Ronnie Tyler in Midsomer Holm, a safe haven for reformed offenders, Barnaby encounters ex-colleague Jack Colby. Jack and his wife Professor Gina Colby live with Lord Holm at Holm Manor. Gina is feted for her work reforming criminals and Jack is now the administrator of the halfway house. The following morning Jack's body is discovered bludgeoned to death. With Jones's help, Barnaby has to go back 16 years to solve this mystery.