A Soviet orbital bomb project threatens the global geopolitical balance. The French secret service contact Francis Mareuil, an aerospace engineer, to recruit the scientist who allowed the bomb to exist.

In East Berlin, Francis discovers that Boris is under surveillance by the Stasi, the East German secret service. He approaches Lyudmila, thinking that she will be able to give him access to his father.

Boris Goloubev directs the space probe to crash in the Algerian desert. When he opposes the Soviet army, he finds himself under house arrest. Francis looks for a way to save Lyudmila.

Repatriated to Czechoslovakia with her injured father, Lyudmila is now threatened by the KGB who are actively looking for her. Francis tries to understand what Boris found in the probe and becomes increasingly estranged from his family.

Anne makes a worrying discovery about Charles Contignet. Lyudmila hides from the KGB, but her only way out is to ask Francis for help.