It is the year of our Lord 1363. And in the cathedral city of York people are dying in mysterious circumstances.
 
But there seems to be a common thread - the herbal remedies dispensed by Nicholas Wilton, Master Apothecary. The first victim is an anonymous pilgrim. But when a highborn nobleman dies after taking the same potion the authorities decide to act.
 
Dispatched to York, in disguise, to unravel the mystery, Owen Archer, former Captain of Archers, apprentices himself to the Apothecary. But it is from Wilton's beautiful wife Lucie that he must learn the arcane secrets of the trade. Slowly but surely Owen begins to uncover the truth. And when the deaths continue he realises to his horror he must count Lucie among the suspects.