John Rawlings, an apothecary in eighteenth century London, is set a task by John Fielding, the founder of the Bow Street Runners, which involves the investigation of a gentleman's club. This club, frequented by members of the upper classes, has a reputation for organising orgies. Rawlings is lucky enough to attend one of the gatherings, but apart from sexual excess, can find nothing terribly wrong until one of the club's members is found dead, apparently poisoned to death. This incident is followed by another murder. Can Rawlings find out what is going on before someone else dies?