An investigation embark on board when the lifeless body of Charlotte Legrand was found floating on a carousel nacelle.

On a canal amidst the "hortillonnages", the floating market gardens of Amiens, a lifeless body is found in a Nautilus-shaped fun-fair gondola. Inspector Monet and his assistant Barnier head the investigation. The victim, a seemingly ordinary woman, was apparently threatened ambitious plans for a Jules Verne theme park.—TV5Monde Europe