In the early 1690s Roger North was preparing to remove from London to Rougham, Norfolk, where he planned to continue his search for truth, which for him meant knowledge of nature, including human nature. But this search was interrupted by three events. First, between c.1704 and the early part of 1706, he read Newton's book on rational (quantitative) mechanics and, afterwards, his book on optics in Clarke's Latin translation. Second, towards the latter part of 1706, he and Clarke, a Norfolk clergyman, corresponded about matters relating to Newton's two books, after which Clarke removed to London and the correspondence ceased. Third, in 1712 North received a letter from Clarke, requesting him to read and respond to his new publication on the philosophy of the Godhead. As Kassler details, each of these events presented a number of challenges to North's values, as well as the way of philosophising he had learned as a student and practitioner of the common law. Because he never made public his responses to the challenges, her book also includes editions of North's notes on reading Newton's books, as well as what now remains of the 1706 and later correspondence with Clarke. In addition, she presents analyses of some of North's 'second thoughts' about the issues raised in the notes and 1706 correspondence and, from an examination of Clarke's main writings, provides a context for understanding the correspondence relating to the 1712 book.