Using a wide range of archival material and a microhistorical approach, Plagues of the heart explores the formation, practice and performance of protestant identity amid the interlocking crises of the seventeenth century. Taking the southwestern port city of Ayr as a remarkable but revealing case study, this book argues that under the stewardship of a generation of radical clergy, Scotland developed a distinct and durable 'culture of covenanting'. This culture was created not simply by swearing the National Covenant of 1638 and the Solemn League and Covenant of 1643, but through reimagining the post-Reformation program of discipline and worship around hard-line interpretations of those covenants. This compelling story of one Scottish town and its remarkable minister offers a fresh understanding of how protestant communities across the early modern world grappled with religion and identity during a remarkably tumultuous age.