Apothecary John Rawlings is intrigued when a letter arrives asking him to investigate an impostor claiming to be the long-lost step-son of a wealthy Bristol merchant in possession of his dead wife's diamond inheritance. John Rawlings' father, Sir Gabriel Kent joins him on the trip to take the healing waters at Hotwell where they socialize with the crème of Bristol society. But Rawlings is compelled to try and solve the mystery and so he must trawl through the underbelly of eighteenth-century society to unearth the sordid secrets at the heart of the investigation.