In her new book, Area 51: An Uncensored History of America's Top Secret Military Base, Annie Jacobsen delves into the nuclear tests and secret aircraft development on the carefully guarded federal preserve in Nevada. But the book's most memorable passages detail Area 51's legacy as purported UFO Central—and, in particular, what happened there after the alleged 1947 crash of a flying saucer near Roswell, N.M. Jacobsen's take veers from the standard conspiracy narrative in just about every imaginable respect: The saucer, she writes, was Russian-made and crewed by human children who were surgically altered to resemble aliens by Nazi death-camp doctor Joseph Mengele, acting at Joseph Stalin's behest.