Carl Fosse, captain of German military intelligence, meets a member of the German Resistance while carrying out a request from his father—a general who took an opposition to Hitler and later took his own life. As a military attaché, Fosse is sent to Lisbon on an underground assignment—to inform the British about the work of the Germans on the atomic bomb. As a representative of the embassy, Fosse is involved in the sale of diamonds, the proceeds from which are supposed to go toward making the bomb. There, arriving under the guise of an employee of the “Shell” company, is Andrea Espinall, a student of mathematics. Her task is to find out how and for what purpose these diamonds are being transported. The characters meet and fall in love—but are spy games meant for lone wolves?