When faced with an unwanted marriage, Alice Rosemeyer accepts an invitation to the estate of Larkhall. Determined to earn her future security without a husband, she begins operating as the anonymous Ace of Hearts, writing letters and offering advice on behalf of the men eager to secure a match at the close of the London season. If she can manage to keep her identity secret, her reputation intact, and avoid the arrogant house guest, Mr. Thomas Herring, she might just call herself successful.

When Thomas Herring's sister marries an indebted man because of a love letter, he has no choice but to marry into money himself. Invited to stay at Larkhall, he sets his sights on the wealthy sister of his host. When she appears indifferent, he stumbles upon an advertisement: a gentleman offering assistance in matters of the heart. An ace, so he is called. But when he turns out to be she, and also a guest at the same house, his task is further complicated—especially as Alice proves herself to be as captivating as she is clever.

With reputations, secrets, and more than one heart at risk, Alice and Thomas become trapped in a game with no rules, a game neither intended to play. Had they been wrong to play love for a fool?