Trapped in a pirated version of a simulated-reality game program, a group of friends nearly have a real tragedy. Arvin plus his mother and six of his ninth- and tenth-grade friends awake in a land of magic and orcs, pledged to rescue a princess. Actually, they're asleep in the basement of computer- whiz Sheldon, who has pirated a quest program. At first, their game follows familiar lines as characters wield their powers to defeat the enemy. Then trouble looms: the program has bugs, while Mom shows signs of a real-world illness that incapacitates her game character and threatens her life. Even so, there's no choice: the game goes on. Continually skirting disaster, the troupe defeats a mock princess, releases an ensorcelled chief mage, and is finally allowed to return home--just in time, since an aneurism in Mom's brain is near breaking. Simulated reality, first seen in adult ``cyberpunk,'' is becoming a trendy plot device in YA fiction (see also recent books by Gillian Rubenstein and Monica Hughes). This succeeds better than most: though there is little development of the technology, the details are ingenious, and having the teen personalities show through their game-character facades is entertaining. The beginning here does hold more promise than is ever realized; Mom's illness and the computer bugs prove to be mostly distractions. Still, the adventures are vivid and diverting. (Fiction. 12+)*justify no*