Boltzmon!

As in his recent Rewind, Sleator's mildly comic time-travel adventure is the story of a boy who prevents his own death by healing family relationships. Computer geek Chris is in perpetual conflict with Lulu, his stereotyped 13-year-old blonde cheerleader sister. She spreads rumors about him at school to increase her popularity, causing Chris to lose his few friends. Then a shape-changing entity called the boltzmon appears, a genielike ""remnant of a giant black hole."" It tells the 11-year-old that the imaginary country he has been creating on his computer actually exists on a parallel earth 40 years in the future. Chris will die very soon in an accident caused by Lulu's conniving behavior unless he goes to this alternate universe and visits some magical Time Temples. Sequences in the primitive and dangerous country contain several exciting escapades (a cannibal kidnapping, a rickety bridge across a chasm), but readers who are sticklers for coherence and logic in their fantasy worlds will be frustrated by the boltzmon's erratic powers and unexplained motivation. ""Here to help you?"" it cries when Chris asks it for directions to the temples. ""Why should I help you? I'm just here to have fun!"" This jolly yet moralizing tangle of a tale is best reserved for hard-core Sleator fans. Ages 10-14. (Sept.)