On a train headed for England a group of travelers is delayed by an avalanche. Holed up in a hotel in a fictional European country, young Iris befriends elderly Miss Froy. When the train resumes, Iris suffers a bout of unconsciousness and wakes to find the old woman has disappeared. The other passengers ominously deny Miss Froy ever existed, so Iris begins to investigate with another traveler and, as the pair sleuth, romantic sparks fly.

Proud Irishwoman Bridie Quilty journeys to Dublin while World War II rages across Europe. During her travels, she encounters J. Miller, who recruits her as a Nazi spy. She acquires the necessary information that leads to the breakout of a German spy who holds key information about the Allies' newest offensive plans. However, the arrival of British officer David Baynes and his romancing of Bridie lead to unexpected consequences.