The story was written by Robert A. Stemmle, Curt Siodmak and Max W. Kimmich, who also presented the idea of this film to his colleagues.

[1] During World War I, young Ellen Lange runs away from her boarding school in Hamburg, because she cannot stand its strict rules any longer, and escapes to her brother Rolf, who lives in Kiel.

She also meets Erik Larsen, a German secret service agent who works under cover at the Lyra publishing house, which turns out to be the hub of the enemy's espionage ring.

As a first step, after returning to Berlin, she tells German counterespionage about the music shop in Copenhagen, and its operatives are rounded up shortly afterwards.

Deeply affected by his death, she gives in to Larsen to take on to another spying assignment with him which leads them both via Copenhagen to London.