Another reviewer put it well, i think, in saying it was a 'ghost of Malorie Blackman's better books.' It isn't great really; even avid Blackman fans like myself, who find themselves glued to jewels like the Noughts and Crosses series, and 'Thief!' will be disappointed in this anaemic read from an author who has produced much better. The story slacks at times; the characters are not sympathetic and Blackman's attempt to bring an adolescent issue into the plot (in the shape of Nova's eating disorder), though valiant, is largely unsuccessful. I wouldn't really recommend it, although if you have read all her other books maybe you should read this one too. But my advice is get it from the library, and save buying the book for passionate, intense works of near-genius like 'Hacker' 'Noughts and Crosses' 'Knife Edge' 'Checkmate' or 'Thief!'
Frankly, if you're a Blackman fan, this second-rater should be well down your list.