A celebrated fashion designer's murder plunges her family into a dangerous investigation during London's bustling social season. Cleo, a young woman with a keen eye for detail, finds herself in the midst of a murder investigation when she discovers Madame Poitiers, the city's most sought-after designer, dead in her salon. As the social season looms, Cleo must navigate a web of secrets and lies surrounding the victim, whose flamboyant persona masked a hidden past. The presence of private detective Harry Armitage's business card adds another layer of intrigue, as Cleo seeks to uncover the motive behind the murder and identify the killer among the suspects, all while dealing with Armitage's evasiveness.

The premise sets up a classic cozy mystery with a historical twist, focusing on a protagonist who uses her observational skills to unravel a murder within her social milieu. The inclusion of a potentially romantic or adversarial relationship with a private detective suggests a blend of mystery and character-driven plotlines. The narrative appears designed to appeal to readers who enjoy period settings, intricate plots, and a focus on uncovering secrets within a closed community. The resolution likely hinges on piecing together clues about the victim's hidden life and identifying the culprit among those who frequented the dressmaker's salon.