Fusing high scholarship with high drama, Anthony Grafton and Joanna Weinberg uncover a secret and extraordinary aspect of a legendary Renaissance scholar’s already celebrated achievement. The French Protestant Isaac Casaubon (1559–1614) is known to us through his pedantic namesake in George Eliot’s Middlemarch. But in this book, the real Casaubon emerges as a genuine literary hero, an intrepid explorer in the world of books. With a flair for storytelling reminiscent of Umberto Eco, Grafton and Weinberg follow Casaubon as he unearths the lost continent of Hebrew learning—and adds this ancient lore to the well-known Renaissance revival of Latin and Greek. The mystery begins with Mark Pattison’s nineteenth-century biography of Casaubon. Here we encounter the Protestant Casaubon embroiled in intellectual quarrels with the Italian and Catholic orator Cesare Baronio. Setting out to understand the nature of this imbroglio, Grafton and Weinberg discover Casaubon’s knowledge of Hebrew. Close reading and sedulous inquiry were Casaubon’s tools in recapturing the lost learning of the ancients—and these are the tools that serve Grafton and Weinberg as they pore through pre-1600 books in Hebrew, and through Casaubon’s own manuscript notebooks. Their search takes them from Oxford to Cambridge, from Dublin to Cambridge, Massachusetts, as they reveal how the scholar discovered the learning of the Hebrews—and at what cost.