Rosalind Thorne has slowly but assuredly gained a reputation as "a useful woman" - by helping respectable women out of some less-than-respectable predicaments. Her latest endeavor is a tragedy waiting to happen. Desperate Margaretta Seymore is with child - and her husband is receiving poisoned pen letters that imply that her condition is the result of an affair with the notorious actor Fletcher Cavendish.

Rosalind Thorne may not have a grand fortune of her own, but she possesses virtues almost as prized by the haut ton: discretion, and a web of connections that enable her to discover just about anything about anyone. Known as a "most useful woman," Rosalind helps society ladies in need--for a modest fee, of course--and her client roster is steadily increasing.

December 1899. After the death of her beloved grandmother, Cleopatra Fox moves into the luxury hotel owned by her estranged uncle in the hopes of putting hardship and loneliness behind her. But the poisoning of a guest on Christmas eve throws her new life, and the hotel, into chaos. Cleo quickly realizes no one can be trusted, not Scotland Yard and especially not the hotel’s charming assistant manager.

Kitty Talbot needs a fortune. Or rather, she needs a husband who has a fortune. Left with her father’s massive debts, she has only twelve weeks to save her family from ruin. Kitty has never been one to back down from a challenge, so she leaves home and heads toward the most dangerous battleground in all of England: the London season. Kitty may be neither accomplished nor especially genteel—but she is utterly single-minded; imbued with cunning and ingenuity, she knows that risk is just part of the game.

Librarian Sylvia Ashe knows nothing about her past, having grown up without a father and a mother who refused to discuss him. When she stumbles upon a diary that suggests she's descended from magicians, she's skeptical. After all, magicians are special, and she's just an ordinary woman who loves books. She seeks answers from a member of the most prominent family of magicians, but she quickly learns that finding the truth won't be easy, especially when he turns out to be as artless as her, and more compelling and dangerous than books.