The Number of the Beast in Revelations is 666; but mathematician Jacob Burroughs has projected a six-dimensional cosmos in which the number of alternative universes adds up to 6 raised to the 6th power and then raised to the 6th again! That's a lot of alternative universes, folks. And--horrors!--one of those universes harbors creatures beastly enough to try snuffing out Jake and his daughter Dejah Thoris (no kidding) at one of Hilda Corners' celebrated parties. So, before you can say "tesseract" Jake, Deety, and Hilda are running--e.g., continuum-hopping--for their lives in the computerized air-car of their polymath rescuer, Zebadiah John Carter. (All this, of course, after a hasty double wedding.) The first part of the book is pretty much standard space adventure with a lot of "in" sf references. And like much of Heinlein, it is noisy, sophomoric, opinionated, and gratuitously sniggery. What gradually emerges, however, is a sort of seriocomic valentine to the genre itself as well as a retrospective Heinlein pastiche that has the rather boresome foursome taking up with the protagonists of the remarkable "Future History" series. . . and finally rubbing elbows, in literal sight of Valhalla, with the likes of Hazel Stone (whom some of us remember from our cradles) and Jubal Harshaw (who showed up a bit later). To reach this charming finale one must plow through several hundred pages of cretinous love-talk and discussions of plumbing arrangements; but it's worth it. Heinlein raised, for better and worse, to the Heinlein-est power.