1940s, Washington, DC. Government girl Louise Pearlie is asked to review the file usage of a missing analyst from the Office of Strategic Services—the United States' wartime intelligence agency—only to learn he'd drowned in the Tidal Basin days before. The OSS confirms it was an accident, and Louise is sent back to her regular job in the file rooms.

Her time spent investigating Paul Hughes at least has one positive outcome, though: Louise meets a young woman in the OSS Reading Room, who asks her to join her "salon," where she is encouraged to talk about controversial issues like racial segregation and equal pay for women. Socializing with the women helps her cope with her beau Joe Prager's transfer to New York City.

But Louise's life soon takes a dangerous and sinister turn, and she can't help but worry if she'll wind up floating in the Tidal Basin herself ...