Gombessa Expedition 4 Laurent Ballesta went to observe a gathering of thousands of groupers during the full moon of June 2014 (Le mystère mérou) in the southern pass of the Polynesian atoll of Fakarava, where he discovered a pack of over seven hundred grey sharks. How can this unprecedented density be explained? Could it be that social behaviors govern this wild horde? During three years of preparation, he and the other divers on his international scientific team tamed their fear by abandoning the defensive reflexes that provoke shark aggression, with the aim of slipping into the heart of the raging pack to study and film it from the inside. Sharks fitted with microchips, receiving antennas, hydrophones, an ark of 32 synchronized cameras...: a whole technological arsenal is mobilized for the project. As the groupers approach for their annual spawning, what battle plan will the sharks deploy?