Twelve linked short stories follow Mr Satterthwaite, an elderly, sharp-eyed socialite who has spent his life watching other people's dramas from the wings rather than living his own. At country houses, restaurants, and gatherings touched by old scandal or impending crisis, he keeps crossing paths with Mr Harley Quin, a tall, elusive stranger who arrives without warning, often in a play of coloured light, and vanishes once his work is done. Quin never explains the cases himself. Instead, through quiet questions and stray remarks, he prompts Satterthwaite to notice what he already half-knows, sharpening the older man's observation until a hidden truth comes clear. Many of the stories circle lovers, broken marriages, suicides, and deaths long misunderstood, and Quin is repeatedly described as a friend to lovers and a figure associated with the dead. The puzzles are real, with concealed motives and overlooked details, yet the tone leans away from the procedural toward something closer to fable. As the sequence progresses, Quin's outline grows fainter and his nature more ambiguous, so that a reader may wonder whether he is a separate man at all or a projection of something buried in Satterthwaite. The Harlequin of the commedia dell'arte stands behind the conception, lending a theatrical, masked quality. Each story works on its own, but together they trace Satterthwaite's slow shift from spectator to participant.
