At an altitude of 4,000 metres. Up there, three young women equipped with all the free-fall equipment have a blast performing aerial tricks, each more impressive than the last. But when they are about to set off their parachute, one of them does not succeed and dies in front of the terrified eyes of her two best friends. In charge of the investigation, Simon and Chloé, played by Flavie Péan, discover that it is not an accident but a murder: the victim's parachute has been sabotaged.