As the dreams of Didier Mathure, a brilliant space engineer, literally go up in smoke when his rocket explodes on take-off, he is transferred to head GEPAN, a unit specializing in UFOs. He is tasked with coming up with scientific explanations for the UFO sightings that are currently dominating the headlines. This is a nightmare job for a die-hard rationalist like him, and he is determined to find a way out as soon as he can.