I has great difficulty reading this within the first 100 pages or so, just because I couldn't get stuck in the plot. However about 200/250 pages in I was glued, personally I would've preferred it if it were like that all the way through but hey ho.
It links well with the previous two books, especially with the Enemy which I found very intruding. Overall an okay book with a mediocre beginning and a semi good ending.
Worth a read if you're a big Charlie Higson fan