A musketeer, a spaniel, and a murder at the most fashionable charity ball of the season — Captain Hastings is invited to Lady Beatrice Mallory's annual costume ball by the charming Anne Foster and promptly arrives with a borrowed sword, a plumed hat, and Pip the spaniel who was not invited but came anyway; among four hundred guests in masks and finery a man dressed as a harlequin is found dead in the palm room, poisoned, costumed, and posed like a joke no one is laughing at, and with an inspector closing in on the wrong suspect, Anne's sharp eye for detail, a stained glove, a blackmailer's receipts, and Pip's inconvenient talent for finding evidence, Hastings must solve a case built on blackmail, embezzlement, and the desperate lengths a man will go to protect the woman he loves; The Corpse at the Costume Ball is an original Golden Age–style mystery about masks, murder, and the discovery that the most dangerous costume is the one a man wears every day.