Lawrence Weschler began spending time with Oliver Sacks in the early 1980s, when he set out to profile the neurologist for his own new employer, The New Yorker. Almost a decade earlier, Dr. Sacks had published his masterpiece Awakenings—the account of his long-dormant patients’ miraculous but troubling return to life in a Bronx hospital ward. But the book had hardly been an immediate success, and the rumpled clinician was still largely unknown. Over the ensuing four years, the two men worked closely together until, for wracking personal reasons, Sacks asked Weschler to abandon the profile, a request to which Weschler acceded. The two remained close friends, however, across the next thirty years and then, just as Sacks was dying, he urged Weschler to take up the project once again. This book is the result of that entreaty.