John Rawlings, the exuberant young apothecary, is celebrating in The Devil's Tavern, a popular if notorious haunt for sailors and smugglers. Stumbling across a corpse that has been fished out of the Thames, he identifies it as Sir William Hartfield, the bridegroom who had failed to show at his own wedding earlier that day.

As the drowning reveals itself as murder, Rawlings is called upon by London's revered sightless magistrate, John Fielding, to investigate the colourful members of Sir William's family – from terrible old Lady Hodkin to her downtrodden daughter, and from Roger, flamboyant man of fashion to the outrageous twins who share an elaborate past.