From the off this engages, confuses & intrigues. Then, rare feat, maintains it for a good 97% of the book! The premise is not just hooky, it's executed really well. The midway twist is a huge change of direction and here flags briefly for that 3% but there's still enough unanswered questions to get the pace back up to frenetic speed. Fleshed out characters & strong ending that I hadn't figured out in advance. V. enjoyable fiction.