By conducting blood tests, Marthe discovers that Ferraud's body is not eliminating the serum and that Sergeant Djibouti's health is deteriorating. Having become aggressive and uncontrollable during his first mission, Gabriel tries to explain to the doctor how he felt. Meanwhile, Colonel Mirreau questions Grüber about the German army's research into another combat serum. The Baron uses Gisèle's esoteric gifts to locate Grüber and prevent him from talking.

The General Staff orders the elimination of the German superhuman, who has become the Sentinels' main enemy. As they set out on his trail, the Sentinels are unaware that they are about to face the Übermensch, an adversary with immeasurable powers...

Irène investigates a news story involving Mirreau that seems to be linked to a state secret. At the cabaret “Les Damnés,” the Baron discovers that Gisèle has run away. After the tragic loss of a comrade-in-arms, Gabriel does everything he can to return quickly to Paris to see his son and wife...

The Sentinels must free Mazauric, the mastermind behind the Dyxenal research, before he hands over vital information about the French serum to the Germans. At Les Damnés, the Baron receives a visit from Diane, a German spy who promises to find Gisèle if he helps her.

On their way to free Mazauric, de Clermont is seriously wounded by a German patrol. Djibouti and Gabriel continue their mission without him and unwittingly draw closer to the Übermensch. At the laboratory, Marthe conducts the first tests on the new recruit, Aria, a young woman sentenced to death, whom she injects with the combat serum.

Irène's investigation has become too dangerous and must be stopped. Held prisoner by the Germans, Gabriel and Djibouti receive help. The Sentinels will have to face the Übermensch, their most formidable enemy...