The year is 1908, and 17-year-old Rosalind Wallace's blissful stay in England with her best friend, Cecily de Vere, has come to an abrupt end. As a publicity stunt, her industrialist father has booked Rosalind on the maiden voyage of his fabulous Transatlantic Express, the world's first railroad to travel under the sea, without asking. Rosalind is furious. Lucky for her, Cecily and her handsome older brother, Charles, volunteer to accompany her home. But fun turns to worry when Charles disappears on the station platform. To Rosalind's surprise, Cecily isn't concerned about her brother. When Cecily runs into an old friend onboard, another belle of the European aristocracy, she appears to forget about Charles altogether. Then, deep under the Atlantic Ocean, Cecily and her housemaid, Doris, are found stabbed to death in their stateroom. Rosalind is now trapped on the train, where nothing is as it seems, in a deadly fight to clear herself of her friend's murder and to thwart a sinister enemy whose ambitions she can only imagine.