Although S. T. Ambler does provide a general survey of the English episcopate in this period, she has written more than just another book about bishops. She asks one central question: why did so many of the English bishops side with Simon de Montfort and against the king in the conflicts of 1264–5? She prefaces her answer by showing how revolutionary a step this was. Neither Langton nor Grosseteste nor Edmund of Abingdon, whose writings and political pre-eminence inevitably put them in the forefront of her exposition, had justified anything more than passive resistance in response to the actions of an unjust ruler. They saw their role as that of peace-makers, while episcopal solidarity, the product of a common intellectual background, common participation in parliaments and councils, and common pastoral concerns, allowed the attitudes of those at the top to be broadly diffused among the whole group. The bishops emerge from her analysis as a generally conservative body, eirenic in outlook and attitude. All these principles were overturned in 1264, when a substantial number were prepared to back Montfort in depriving the king of power: a volte-face which Ambler ascribes to the charisma of Montfort as a leader and as a fighter for the justice and righteousness which were fundamental to the bishops’ convictions. This is a notably coherent and well-structured argument. It rests in the first place on a rigorous analysis of texts, especially Langton's theological writings, Grosseteste's commentary on the Nicomachean Ethics, the Song of Lewes, and the dossier concerning the activities of the papal legate in 1264, which is one of the book's strengths. Close work on other sources enables the author to overturn some widely accepted views. She is at her most original in demonstrating convincingly (contra this reviewer) that these strikingly unradical bishops did not side with the reformers from the start, in 1258, but were drawn into the movement in two later stages: first, with the Provisions of Westminster in 1259, which even conservatives could support since the Provisions promised justice and had the king's assent, and then, at a second stage, with the emergence of Montfort as the movement's sole leader in 1263–4. The case is to a degree overstated, since the Montfortian bishops never constituted more than a minority of the whole episcopate – a point to which Ambler should perhaps have given greater weight. Yet these men had a significance which was out of proportion to their numbers, not least in providing some precedents for future episcopal actions. To those which she considers might have been added the major part played by the bishops in Edward ii’s deposition. But these are trivial criticisms of an excellent book, bold in its range and persuasive in its reasoning. Before it appears as a paperback (as it surely will) one minor error should be corrected. In 1258 the bishops met, not at Merton in Oxfordshire, an isolated marshside village (p. 107), but, much more fittingly, at Merton priory in Surrey.