1978. Didier Mathure, a brilliant space engineer, is transferred to GEPAN, a unit specializing in UFOs, run by a team whose members seem to be living on another planet themselves. After seeing a UFO for himself, which has unsettled his ultra-rational mind, Didier is now travelling the country in the hope of new sightings... in vain. He's about to give up when a strange phenomenon occurs at a nuclear power plant. It's a challenge for the GEPAN team, who find themselves overwhelmed by this mystery that people find so fascinating. Convinced that an extraterrestrial being is trying to make contact, Didier will do all he can to answer, unless Claire Carmignac from the Ministry of Energy gets in his way...