Joseph Skledowski, an apothecary taking refuge in England at the time of the Civil War, becomes disillusioned with the efficacy of the medicines of his trade and sceptical of its underlying philosophy. An accident brings him a revelation that leads him to question his alchemical assumptions and sets him on a faltering path towards scientific rationalism. The new life does not does not rid him of old and deadly enemies, inherited from his mentor, who believe him to possess valuable secrets; nor can he avoid the ravages of the Great Fires of Bristol and London. With the new life come discoveries and dangers, along with immense satisfactions, profound problems and a difficult love affair.