Building on the work of Peter Biller in particular, as well as Georg Modestin, Alexander Patschovsky, and Peter Segl, among others, Reima Välimäki's book adds significantly to our understanding of the church's efforts to repress the Waldensian heresy in late-medieval Germany. His study focuses on the role played by the Celestine monk, inquisitor, and polemicist Petrus Zwicker. In addition to serving as provincial of the Celestine Order in Germany, Zwicker also conducted multiple inquisitions against Waldensians between 1391 and 1404, including at Erfurt, Stettin, Vienna, and Buda. Välimäki's examination of the sources, including dozens of manuscripts, results in important contributions to our knowledge of Zwicker as an anti-Waldensian polemicist and inquisitor, not the least of which was the key role he played in what Välimäki calls a “pastoralization” (5) of heresy in the context of the Roman Catholic Church's Great Schism (1378–1417).

Petrus Zwicker's authorship of the polemical treatise Cum dormirent homines (While Men Slept) on the errors of the Waldensians has been established by Peter Biller. Välimäki demonstrates that a related treatise known as the Refutatio errorum was also authored by Zwicker. He hypothesizes that Zwicker wrote the Refutatio, summarizing Waldensian doctrines alongside orthodox counter-arguments, for the inquisitors with whom he worked to use when interrogating suspected Waldensians, whereas the Cum dormirent homines (for which the Refutatio may have served as a draft) was a more polished treatise intended for wider pastoral use, and indeed survives in about fifty manuscript copies, compared with nineteen (often alongside Cum dormirent homines) for the Refutatio. In addition to these treatises, Zwicker produced and continued to revise a compilation of texts (questionnaires, lists of Waldensian errors, examples of sentences, and penances assigned to convicted heretics) he used as a working manual when conducting inquisitions. Based on comparison of the nineteen manuscripts of this so-called Processus Petri (a label coined by Biller) bound with copies of the Cum dormirent homines, Välimäki identifies one version of this compilation (Stift Sankt Florian MS XI 234) as the version Zwicker prepared specifically in conjunction with the inquisition he undertook in 1395–1398 in the diocese of Passau.

Analyzing the Cum dormirent homines, the Refutatio errorum, and the Processus Petri in particular, but also other sources including the surviving protocols from the 1392 inquisition trials Zwicker held at Stettin, Välimäki argues that Zwicker bears a primary responsibility for a pastoralization of heresy during the decades around the turn of the fifteenth century, alongside Martinus of Prague and other inquisitorial colleagues in central Europe. Alongside the concern of rooting out heretics, this pastoral approach was designed to promote doctrinal orthodoxy within the broader clerical and lay communities. One component of this pastoralization was Zwicker's emphasis, when examining suspected Waldensians, not on their actions or social networks, but on their beliefs regarding such matters as purgatory, the efficacy of prayers for the dead, the intercessory powers of the saints, and the sacramental authority of the clergy. As both inquisitor and writer of anti-heretical treatises, Zwicker wanted not only to correct and eliminate Waldensians, but also to address doubts among the orthodox concerning the dignity of the clergy and the authority of the church's sacramental theology and ritual practices.

A second aspect of Zwicker's pastoral approach was to rely primarily and explicitly on biblical passages when constructing his arguments in support of the church and clergy against Waldensian critiques. This reliance on scripture alone to provide supporting texts justifying the various cultic and doctrinal traditions of the Catholic Church aligns with a pastoral need, widely evidenced from the late fourteenth century on, to demonstrate the unity and antiquity of the orthodoxy preached and enforced by ecclesiastical authority. As Välimäki demonstrates, Zwicker's anti-Waldensian polemics successfully combined a polemical style drawn from anti-heretical polemics of the thirteenth century with a fourteenth-century reliance on biblical interpretation to address challenges to ecclesiastical authority. This connects to what Välimäki identifies as a third way in which Zwicker contributed to the pastoralization of heresy: the incorporation of Zwicker's writings into such early-fifteenth-century pastoral works as Ulrich von Pottenstein's German-language catechetical treatise and the sermon collection of Johlín of Vodňany.

Although Zwicker does not mention the Great Schism in Cum dormirent homines, Välimäki accurately and insightfully places the inquisitor's career and writings into this context. Zwicker contrasted the unity, universality, and temporal continuity of the Catholic Church from the time of Christ and the apostles with the sectarian divisions, isolation in small numbers, and postbiblical origins of the Waldensian heretics. Persecuting the Waldensians, therefore, was a way for Zwicker and others to translate any doubts about church teachings or ritual practice into potential heresy. It also enabled the clergy to deploy the persecution of dissidents as a way to quell their own doubts and anxieties resulting from a persistent crisis in ecclesiastical unity and stability that, during Zwicker's lifetime, seemed far from resolution.

Välimäki is very much aware that Zwicker's pastoralization of heresy required not only the participation of inquisitors, but also the publicly disciplined bodies of persecuted Waldensians. The trials over which the Celestine monk and provincial presided resulted in condemned heretics suffering such punishments as humiliating penance, perpetual imprisonment, and burning at the stake. However, while acknowledging the experiences of those tried and convicted by Zwicker and his fellow inquisitors, this is not a study centered upon the men and women who embraced and persisted in a Waldensian identity in the face of ecclesiastical persecution. It concentrates on understanding the motives and anxieties of devout members of the clergy striving to uphold a vision of ecclesiastical unity and spiritual integrity in a context where the Great Schism showed no sign of coming to an end. In this respect, Välimäki argues persuasively that the work of Petrus Zwicker deserves to be better known as a representative and influential articulation of what hunting heretics meant to an inquisitor in the service of a sorely divided church.