In a high mountain refuge, Alex Hugo discovers the bodies of Isabelle and Antoine Lindberg. A farewell letter gives details of the circumstances of their death. Isabelle, who was suffering from an incurable disease, wanted to end it. Antoine decided to accompany him on his last trip. The couple asks that their ashes be scattered at the top of the mountain. But Alex is not convinced by these too simple explanations. He wonders if someone would not have made up a double murder in suicide. He begins a delicate investigation...