Jean and Charlie are opening their new antiques shop, but the celebration is interrupted by the news that Jeremy has been taken to the police station. The body of a young woman is found on a cabin cruiser, but is he to blame?

Jean and Dom assist Caron in solving a murder in a beautiful but remote country mansion. Robert Coste lives in the house with his devoted housekeeper and his troublesome son. He has recently sold the house to Jeremy and Judith and is moving to Paris. As Jeremy and Judith arrive to start refurbishing their new investment, a gunshot rings out. Judith races into the house and is horrified to find Robert shot at his kitchen table, clasping a unique key. Did someone not want him to leave? And why did he ask his neighbour to sign his new will only the night before? When Caron calls Jean to help, she finds herself in a house full of the most beautiful antiques and can't wait to discover what the key could unlock. But first someone needs to persuade Jeremy and Judith to leave! As Caron and Gendarme Richard set up an incident room in the mansion, Jean explores the house, trying the key in every lock she sees. It's a huge task and the eventual truth is unexpected — even for Jean. Caron is convinced that the killer will return and when he suggests to Jean that they set up a stakeout that night, Dom is eager to join in. Will the murderer walk into Caron and Jean's trap? And with Jeremy and Judith anxious that an inconvenient murder doesn't derail their refurbishment, why does Dom really want to help Jean out? Meanwhile, love rolls into town for Gloria when a mystery man brings his car to the garage, but her newfound happiness has an unexpected effect on her friends. Will she have to choose between friendship and love? An isolated murder, a midnight stakeout and love in the air… all the elements of a classic murder mystery in Sainte Victoire!