Didier Mathure, a brilliant space engineer, has not recovered from the explosion of his CRISTAL rocket, which he is appointed against his will to head GEPAN, a group for the study of unidentified aerospace phenomena. A rain of pink flamingos is at the origin of the first mystery that he needs to solve.

The GEPAN, in turmoil, is preparing for the big ufological meetings where the team must make a good figure. Didier resolves to accept a deal with Commander Delbrosse, of Military Security, to obtain information. Marcel confides in Didier: the postcards sent by the former director of GEPAN make it possible to identify witnesses of an unknown phenomenon, who have mysteriously disappeared.