The main story takes place over the course of about a week in May 1555 during the reign of 'bloody' Mary Tudor.
In part one, the first and now former Bishop of Bristol, Lord Paul Bushe, is alerted to a mounting heresy problem developing in Kingswood Forest (a wild part of the diocese of Bristol) by the inexperienced new bishop, Lord John Holyman. He is called away from his comfortable and established routine as Rector of Winterbourne and the simpler life of a country gentleman scholar to investigate and resolve the matter before it attracts national attention. The situation raises apprehension and genuine fear, and Bushe agrees to act in order to protect the diocese and its environs from the dire social, economic, and religious consequences of the queen's (rumoured) heightened zealotry.
Bushe's thoughts, travels, and decisions are juxtaposed with those of Master John Burgess, a budding force in the local woollen industry and a well-liked man of Kingswood Town. As Bushe moves toward Bristol Cathedral, he reminisces about his life as a chaplain to Henry VIII, as a bishop, and as a client of Thomas Cromwell. Interspaced with these are segments on Burgess's travels to Mid-Summer Norton and Wells (which took place about a year earlier), his instructing of his apprentice in the wool trade, and about life in general, discussions of current events, meeting both his contacts in the banned book network and his first run-in with England's changing religious laws. At the end of part one Bushe meets with Burgess in the cells of Bristol Cathedral in order to make an assessment of his character and culpability. He finds that the real driving force behind the growing heresy is not John, however, but his wife Margaret (currently in the next cell over).
In part two, the story follows Bushe's investigation of the heresy matter, a journey which takes him to Kingswood Town, Bitten, and back again to Bristol. Here, his movements are juxtaposed with the investigation, with Bushe's interviews with Margaret in the Cathedral cells, their discussions of the main religious issues (theology and bible passages), her leading of a small prophecy fellowship at one of her husband's woollen mills (featuring members of the fellowship), the effect her group is having in the town and the threat to the diocese and the region that it inspires. Over the course of the investigation Bushe finds himself impressed with Margaret's enthusiasm (if not her actually understanding of the issues) and tries to give her the benefit of his greater learning and wisdom (wishing that he could teach her a better way). Early on Bushe accuses Margaret of being the biblical and titular unprofitable servant, but over the course of their meetings and events which transpire he comes to wonder if perhaps he was not actually himself the servant. The Burgess case gives Bushe a final chance to prove to himself that he is not and to do something genuinely beneficial.
Part three is the final confrontation, at the Cathedral, between Bushe, the Burgesses, and the members of the Kingswood Town fellowship. Here Bushe tries to bring them around the a correct understanding of the Marian constituted religion, in the process saving their souls and sending them back out with a heightened sense of truth and a desire to work for the betterment of the forest folk in a more royally-approved manner. The Epilogue is Bushe's beginning to finally write the treatise he has been tasked by the queen and archbishop to write, one which uses the recent events as both starting point and subject matter, meant to bring a wider understanding of the issues to the realm at large. Bristol, England's second city and home of the woollen industry, is spared from the burnings.
