March 1916: The First World War has been raging for almost two years. There is no end in sight.
Wilhelm should actually be winning this war as a front-line officer for his fatherland. But because rumors about his sexuality made the rounds a few years ago, he was expelled early from the Naval Academy. Since then, he has eked out an existence as a lowly cryptographer in an open-plan office - until he finally gets the chance to prove himself.
To crush the Western Front, the German Empire wants to spark a revolution in Ireland, an English colony that has been exploited for centuries, thus weakening Britain from within. To do this, however, Berlin must supply the Irish rebels with weapons. Wilhelm's mission is to sneak into Dublin as a spy and establish encrypted radio contact between the rebels and Berlin in order to ensure the smooth running of the arms delivery.
Highly motivated, Wilhelm travels to the Irish capital under the stolen identity of a teacher. By day he teaches at the local boys' boarding school run by the leader of the Irish underground, and by night he exchanges coded telegrams with Berlin.
However, when his simple task fails to bring him the fame he had hoped for, Wilhelm oversteps his authority and takes ever greater risks to ensure the success of the revolution. In doing so, he attracts the attention of an English inspector, who from then on does everything he can to expose the German spy. When Wilhelm develops feelings for an Irish teacher, the already tense situation threatens to spiral out of control.