*The Number of the Beast* is a mind-bending experiment by one of the greatest writers in science fiction who ever lived and the author of the classic bestseller, *Starship Troopers*. It is a parallel book about parallel universes. Most readers did not realize in 1980 (when it was originally published) that the novel had a sister book, written in 1977, that was never published. That book is finally being published under the title *The Pursuit of the Pankera*. . Both novels deal with parallel universes, share the same main characters and have the same first one-third of the book. However, from that point on (after they make a jump to a parallel universe) the novels diverge completely. . And here is where the second part of the experiment comes in. While *The Pursuit of the Pankera* continues the adventure in a very customary Heinlein manner, reminiscent of his earlier works, *The Number of the Beast* becomes something very different. . On surface, the book is about two men and two women who are attacked by aliens and then embark on roller coaster ride of an adventure through a myriad of universes. But as Jack Kirwan wrote in *The National Review* , “describing *The Number of the Beast* thus is like saying *Moby Dick* is about a one-legged guy trying to catch a fish.” *The Number of the Beast* is a homage to science fiction, to his friends and to characters used in other books, also serving as a parody and a lesson to anyone willing to listen, in a way only Robert A. Heinlein could have presented it.