The Giant Oarfish, the largest bony fish in the world, was known only by rare examples that died by stranding, as well as one sole fossil. Its extraordinary dimensions, as long as 15 meters, and shape in the form of a silver ribbon, inspired the myth of the sea serpent. For the past two years, scientific buoys, immersed at a depth of two thousand meters in the Mediterranean, off the French Riviera, have attracted countless species of pelagic fish ; among them, the Giant Oarfish drifting vertically, alone or by pairs. With the help of the world expert in Giant Oarfish and logistic collaboration of enthusiasts, a scientific expedition reveals the biology of this enigmatic ambassador of the abyss. Entirely shot in Ultra High Definition, the film raises the veil on its paradoxical habits: why do all the adults self-mutilate and rid themselves of two-thirds of their bodies without being affected? How do they meet in the immensity of the ocean? Why does this fish not have any known predators?