To avoid diplomatic confusion, she is kidnapped while dancing with Austro-Hungarian General Staff Captain Michael von Homberg at a ball held at the famous Hotel Sacher in Vienna, and sent back to Italy.

Shortly afterwards, a secret plan of an Austrian fortress appears on von Homberg's office desk, and as he himself is unable to explain this, the Evidenzbureau urges him to commit suicide, but he instead manages to escape from Vienna and goes on the run.

Returning to Vienna, von Homberg asks his former superiors for a chance to clear his name, and is given a Royal Italian Army uniform and tasked with flying to Italy to find the traitor who put the plans on his office desk three years ago.

After he recovers, von Hombergk takes a train to Rome, intending to speak with Ermete Davila, an antiques dealer and faithful Austrian agent, and meets a suspicious man named Bluentzli.

Von Homberg manages to return to his hotel room without being discovered, but finds Bluentzli waiting for him, who proceeds to blackmail him with knowledge of his affair with Marcella.

Wíth the aid of Bluentzli, von Homberg arranges to pilot the aircraft which will fly K 77, who he discovers is a high-ranking Austro-Hungarian General Staff officer of Italian origin, back to Austria.