Calista Langley operates an exclusive "introduction" agency in Victorian London, catering to respectable ladies and gentlemen who find themselves alone in the world. But now, a dangerously obsessed individual has begun sending her trinkets and gifts suitable only for those in deepest mourning. Desperate for help Calista turns to Trent Hastings, a reclusive author of popular crime novels. It becomes clear that the danger may be coming from Calista's own secret past.