Right up there with City of Dark Magic (also published by Penguin) a certified mess of a book/plotting trying to be too clever with every genre out there spliced into a 500 page book and the first of a trilogy as well, for good measure.
Could have been done with it in less than 400 pages and with more clarity in its pacing. (Larger fonts for YA readers?)
Still doesn't explain much on its minimalist time-travelling premise.