Back in Brittany, Captain Morgane Ledantec is confronted with the discovery of human bones after the fall of a sacred oak during a storm. The victim was a follower of druidism which Morgane was introduced to as a teenager by her godmother.

Captain Jérémy Laubier investigates a young surfer's murder in La Torche, Breton, discovering a course on Ys myth. Professor Morgane Le Dantec identifies the victim's sister.

Under the musical direction of Nach (Anna Chedid) , more than twenty artists gathered to celebrate Balavoine for a day in magnificent locations in Biarritz, the city where he grew up and to which he maintained lifelong ties. They all shared one thing in common: without Daniel Balavoine, they would not have become the artists they are today.