Military Intelligence dismisses the picture as insignificant, but in the state of emergency Stalin suspects a German plot. He summons his old adversary, Inspector Pekkala - the elusive Finn who was once Tsar Nicholas II's personal detective - to discover the real significance of this strange wartime cargo.

As Hitler's forces smash into Soviet territory, annihilating the Red Army divisions in its path, a lone German scout plane is forced down. Contained within the briefcase of its passenger is the seemingly inconsequential painting of a hyalophoria cecropia, otherwise known as a red moth.