Myrtle Hardcastle would rather stay at home to keep close tabs on criminals and murder trials than go on a relaxing vacation with her aunt Helena. Once on board the luxurious private railway coach, Myrtle is thrilled to meet Mrs. Bloom, a professional insurance investigator who is tasked with protecting the priceless Northern Lights tiara. But before the train reaches its destination, both the tiara and Mrs. Bloom vanish. Then a dead body is discovered in the baggage car--stabbed with Aunt Helena's sewing scissors. Myrtle tries to discover which of her fellow travelers is a thief and a murderer.