Tad Williams began his Otherland series with the massive City of Golden Shadow and continues it with the equally hefty River of Blue Fire. Williams says it will require four (big) books to tell his complex, multithreaded tale, and at the rate that the plot of this second novel moves, readers will see what he means. Not that the book is a slow read; in fact, River is as much a suspenseful page-turner as the first book. As River opens, we join up again with the ragtag bunch of searchers trapped in an astoundingly detailed and frightfully dangerous virtual world known as Otherland. Lurking in disguise among the group is the brutally vicious serial killer Dread, trying to find information that will help him overthrow his Grail Brotherhood masters. The group follows a ubiquitous river through world after world, unable to go offline, and subject to the increasingly terrifying certainty that things in this supposedly virtual place are all too real. Meanwhile, Paul Jonas, an amnesic (but somehow pivotal) character fleeing from two sinister beings, finds more and more of his memory as he does his own Huck Finn river trip. As in the first novel, each new world that the characters enter, from Paleolithic Ice Age to something suspiciously like Oz, is fully realized and completely unpredictable. Williams is a master at parceling out information to the reader in dribs and drabs, which is frustrating yet tantalizing, like a particularly good computer game. When the group is split up and the adventure divides further, the reader senses the author as a puppet master, following some incredibly complex flows of information. The best course is just to hang on and enjoy Williams's deft characterizations, lush descriptions, and wildly divergent plot. If you've ever been white-water rafting, you'll recognize the feeling. --Therese Littleton