The Spider and the Fly (1949 film)

The Spider and the Fly is a 1949 film directed by Robert Hamer. An unusual love triangle develops between two criminals and a policeman on the eve of World War I.

Finally, Maubert gets the break he has been waiting for. Lodocq employs Jean Louis brother Alfred for his next theft. Maubert gets Alfred to betray Lodocq, not out of revenge, but by telling him that Lodocq did not give his mother Jeans fair share of the loot a lie. Lodocq is imprisoned just as World War I breaks out.In the war, Maubert becomes a major in French counterintelligence. When the Minister of War Edward Chapman tells him that they urgently need a list of German spies in France being kept in a safe in the German embassy in neutral Berne, Switzerland, Maubert states there is only one man for the job. Maubert is authorized to offer a pardon to Lodocq in exchange for his services. The prisoner agrees after Maubert dangles the prospect of seeing Madeleine. ........

Source: Wikipedia