February 1965. A Soviet orbital bomb project threatens the global geopolitical balance. Francis Mareuil, an aerospace engineer, is contacted by the French secret services to recruit Boris Goloubev, the scientist who allowed this bomb to exist. In Moscow, the KGB organizes surveillance of Boris by forcing his daughter, Lyudmila, to spy on him.

In East Berlin, Francis discovers that Boris is under the permanent surveillance of the Stasi, the East German secret service. He approaches Lyudmila, convinced that she will be able to give him access to his father, but unaware of his links with the KGB.

Lyudmila is back in Czechoslovakia with her wounded father, and in danger: the KGB is tracking her down. Francis tries to understand what Boris found in the probe and retreats further and further away from his family.

Lyudmila is alone and stuck in Czechoslovakia. Francis reconciles with his wife and takes part in a mission co-speared by the SDECE and the CIA, with a common goal: to contact Boris.

While investigating Charles Contignet, Anne makes a troubling discovery. Hunted by the KGB, Lyudmila hides with a Czech family. There is only one way out for her: to contact Francis and ask him to come save her.

In Czechoslovakia, Francis jumps through hoops to find Lyudmila. As they try to get back West, Yemelin and his henchmen chase them down. Anne finds a top-secret document and is now in danger. She must flee.

As the orbital bomb is about to crash, Francis, Lyudmila and Anne risk capture and death. Yemelin, through powerful allies in France, will do anything to get the numbers back, as well as the list.