That’s the set-up for what becomes a gripping and disturbing thriller. It’s gripping because it tells a good story, and offers a puzzle to be investigated in the classic style of this kind of fiction. In the modern manner it is a bit wordy, scenes prolonged after the point has been made, though readers capable of understanding the hi-tech and scientific jargon and long explanations of how Make-Believe works may not share this reservation. But it’s a classic quest novel and Cassie is an engaging and credible character. Moreover, though they may skip some paragraphs because they don’t understand anything of what they are being told, the plot is strong enough to hold any reader’s attention.