Over the centuries, Mont Saint-Michel, an extraordinary island located in the delta of the Couesnon River, in Normandy, France, a place floating between the sea and the sky, has been a sanctuary, an abbey, a fortress and a prison. But how was this architectural wonder built?

A seemingly mystical murder takes Captain Sophie Maliquot back to the Mont-Saint-Michel region where she spent part of her childhood and where her father, who died years earlier, is buried.

After the death of his mother, Elisa (Claire Borotra) is responsible for custody of her sister Audrey (Penelope Leveque), a troubled teen and something he hardly knows. Following the last will of her mother, both go to Mont Saint Michel, where the two grew up, to spread his ashes. The second night of stay, and after a flood, Audrey disappears while the mayor's daughter, which suggests a voluntary escape, but Elisa does not think so, so it will not stop until its trace sister.

The magnificent Mont Saint-Michel fortress has stood in the middle of a bay off the French coast of Normandy for centuries. It has come to symbolize a stubborn resistance to the passage of time and to the turbulence of European history. This film journeys through the history of this indomitable fortress going back to the 8th century AD. Explore the legends that surround this timeless masterpiece.