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!

Loud rock music is paying at the Château and it's giving Judith a headache. Jeremy's old rock ‘n' roll friend Dura is recording his comeback album in the Millhouse. Jeremy locks him in and leaves him to work alone - but not before insisting on taking a selfie. Outside, in the sound van Dura's wife Mandarina, and Marco, his sound engineer, have just started to record Dura's latest track when they hear him scream. Forcing their way into the Milhouse, the trio find Dura lying dead with a head injury. A strange symbol is drawn on his face. How could he have died in the locked room alone? Caron calls in Jean to try to make sense of it all. At La Couronne, Trevor is meeting Cooper for the first time when Jean receives Caron's call. Dom and Trevor are both huge Dura fans and are horrified to hear that he's been murdered. When Jean and Dom go into Dura's studio, Dom is overwhelmed to see Dura's original speaker and can't help but touch it. Could that be a tear in his eye? Chloe made the lucrative deal with Mandarina for Dura's album. She arrives in Sainte Victoire for the first time to tell Mandarina that the record company are demanding their money back. Mandarina and Marco are outraged and Judith throws Chloe out. That evening Dom is at Jean's house trying to impress her with his collection of original Dura albums. Jean is intrigued and starts to investigate this strange murder. Can Jean and Dom find out what really happened and discover who would want this rock legend dead?