In 1942, while living in Switzerland, Bancroft was recruited by the Office of Strategic Services, and both worked and had a romantic relationship with Allen Dulles.
Her most important work was with Hans Bernd Gisevius, a German military intelligence officer who supplied her with details of the 20 July plot to assassinate Hitler.
[2] She moved to Zurich, Switzerland in 1934, where she learned excellent French and German,[4] and became a close friend and student of Carl Jung, who cured her of chronic attacks of sneezing.
[6] Following the US entry into World War II, Bancroft was recruited by the Office of Strategic Services, although she was not initially aware of the fact, being asked by a US Embassy contact to write analyses of German policy based on German public sources for Swiss and American newspapers.
She became "a leading champion of Jung's psychology in the United States",[4] lecturing on the subject and publishing articles in academic journals.