September 1985, at a depth of 36 meters at the bottom of a rocky drop off in the creeks between Cassis and Marseille, the eye of the diver Henri Cosquer, known as Barbu, is attracted by a discreet opening in the rock. With his experience, he leaves the big blue to explore the first meters of this mysterious conduit where total darkness quickly reigns!
The following days, he progresses deeper and deeper with only the indications of his diving instruments and the beam of his lamp.
But where does this gallery lead?
What is it hiding?
Does it only have one way out?
Faced with the unknown, Henri acts instinctively but he knows nothing of what he can discover in this endless drowned hose …