As the 1910 London Season comes to an end, it's time for Lady Theodora Prescott-Pryce's annual pilgrimage to visit her cousins in Scotland. Accompanied by only her maid, Molly, she thinks she's in for another long, dull trip aboard the Flying Scotsman.

The last thing she expects to find as they departed from London is a body in her compartment. Despite Molly being accused of the murder, Thea knows her maid is innocent. Aided by a young Scotland Yard inspector and an American heiress, Thea uses the detective skills she learned from reading Sherlock Holmes to track down the real murderer, but will she find them before they can strike again?