February 1913. Lady Hardcastle and her diminutive but brave lady’s maid, Flo, have been invited by their friend JB McIntyre to spend the weekend at his recently renovated Tudor fort on a remote island off the Devonshire coast. But the holiday quickly turns sinister when first a number of valuable jewels go missing—and then a fellow guest is murdered with a most unusual weapon.

Asked by JB to investigate, the stakes are raised for the sleuthing duo when a violent storm traps the group on the island and cuts them off from help. Is the murderer in their midst? With everyone claiming to have an alibi—but each also having a skeleton in their closet—can Lady Hardcastle and Flo unravel this complex web of secrets and deception before the killer strikes again?