For the last century the legend of Grigory Rasputin—that of a lascivious peasant who breathed religious fervor, held the Romanovs in mystical thrall, and single-handedly brought down their empire—has seemed as immortal as the man himself was said to have been during his own murder, which conventional accounts claim required extraordinary effort to slay an almost supernatural being. In Rasputin: Faith, Power, and the Twilight of the Romanovs, a doorstopper of a book clocking in at over 800 pages, Douglas Smith tries to make sense of Rasputin as both a man and a phenomenon. Already the well-regarded author of a brace of excellent books on the fate of the Russian nobility through the ages, he has taken up the challenge of demystifying the mystic and writing his proper place into the history of his country.

Six years of painstaking research took Smith not...