Otherland 3 Mountain of Black Glass by Tad Williams.
Part 3 of the cyberpunk saga Otherland. The Grail Brotherhood has built the most powerful, sophisticated simulation network imaginable. At the same time, they have manipulated and injured the minds of thousands of children.”
This proclamation from the mysterious Mr. Sellars confirmed what Renie Sulaweyo had feared to be true when she first broke into the Otherland network in a desperate search for the cause of her brother Stephen’s deathlike coma.
Now Renie, the Bushman !Xabbu, and their companions find themselves navigating a treacherous and ever-changing course – from a strangely unfinished land, to a seemingly endless labyrinthine House – pursuing a sociopathic killer who has stolen one of their group. To Renie’s despair she is no closer to uncovering the secrets which could help save Stephen’s life, and now it appears that something may be very wrong with the Otherland network itself.