Paulsen (Brian's Winter) works his magic with another wilderness adventure yarn. But the wilderness this time isn't in this world--or is it? That's what 13-year-old Mark tries to discover. On his first solo backpacking trip, crossing an old missile range in a desert out west, a mysterious blue light transports him to a thick red jungle under a sulfurous sky. There the struggle for survival soon supersedes the quest for the route home. Paulsen draws on such Saturday-matinee staples as poisonous insects, deadly quicksand and murderous beasts; Mark even swings on vines with a friendly monkey-like creature (and this is just the first 30 pages). Yet the plot feels fresh, thanks to the author's taut, unsentimental storytelling (Mark's Tarzan-esque antics, for example, result in broken ribs). Mark grows to manhood in the four or so years of his sojourn; the narrative, meanwhile, continues at a hurtling pace. The teen saves a girl's life, then joins her tribe of forest-dwellers; later, he is captured with them and enslaved by the more technologically advanced Tsook people. There are raids, escapes and brushes with the Tsook overlord, the Merkon, who takes a frighteningly keen interest in Mark. Readers may figure out who the Merkon is long before the protagonist does, but no matter--the action along the way (including just the right dash of romance) is never less than enthralling. While the story is self-contained, the end points to a sequel, so, with any luck, another installment is on the way. Ages 12-up. (May)