After a mission with the Red Cross on the Western Front, nurse Johanna Gabathuler returns to Davos pregnant. While she is still in the delivery room, her father takes her newborn daughter away from her. To get her back, she will have to make a deal with German secret services.

During the traditional New Year's Eve ball, when the drama of war takes a break, Johanna must carry out a risky assignment as a spy. However, the situation becomes critical, putting the nurse and her family in grave danger.

Johanna and Ilse discover the meaning of “Mission H”. The nurse must then prevent a mysterious Swiss Army encryption device from falling into the wrong hands, but her sister becomes suspicious when she finds weapons and money in her room.

General Taylor's hasty departure makes Johanna useless as an informant for German intelligence. Ilse is then given the task of eliminating her, without realizing that she is always one step behind.

While the hunt for the traitor responsible for the explosion begins, Johanna does everything to ensure the implementation of the "Lenin Plan", which involves a revolt against the Tsar in order to get Russia out of the war.

Johanna and Mangold would like to get out of the espionage ring, but the doctor is captured during the preparations for the escape. Accused of treason, Johanna is therefore forced to prove her innocence by collaborating in the delivery of money to Lenin.