North by Northeast — Phyllis A. Humphrey

Haley Parsons, a school teacher on her first real vacation in years, boards the beautiful and luxurious American Orient Express for a week-long train excursion from New Orleans to Washington, D.C.. But then her jewelry begins to disappear and she finds herself an unwitting player in a kidnapping and robbery attempt. The culprit is evidently aboard the train; and Jonathan Shafer, Haley's handsome, newfound love interest, is somehow involved. Who is he, really? And what part will he play in all this?