Stamboul Quest

Stamboul Quest is a 1934 spy film set in World War I, directed by Sam Wood, starring Myrna Loy and George Brent and featuring Lionel Atwill. The screenplay was written by Herman J. Mankiewicz from a story by Leo Birinski.

As his best agent has not been heard from in several weeks, von Sturm assigns Kruger Leo G. Carroll the task. Shortly afterwards, Annemarie Myrna Loy, known by the code name Frulein Doktor, returns after completing her mission. She also informs von Sturm that fellow spy Mata Hari has fallen in love and therefore can no longer be trusted. She recommends that an incriminating message be sent using a code that she knows has been broken by the Allies. In addition, she uncovers Kruger as a British double agent known as K6.When Kruger is arrested at his dentist contacts office, another patient, American medical student Douglas Beall George Brent, is also taken into custody, though he is later released. Just to be sure though, von Sturm orders Annemarie to make sure Beall is innocent. She arranges to be rescued from an unwanted suitor by Beall, who invites her to his hotel suite. During the course of the evening, he confesses he has fallen in love with her, now going by the name Helena Bohlen. Helena is attracted to him, but when she reads a coded message from von Sturm informing her that he has taken her advice regarding Mata Hari, she abruptly leaves. ........

Source: Wikipedia