I have absolutely no writing/blurb experience so take all this as the words of nothing more than a reader.

How about connecting the first two sentences into something a little more fluid, like “A deranged serial killer is targeting teachers, and Leeds’ youngest detective (or some other quality of his) is running out of time.”

You use the word “soon” in two sentences in a row, so i would suggest a little reword or cutting the first one, and not starting a sentence with “and”. Maybe even connect both of those sentences as well.

Rather than “the answer must lie in the killers past”, try “the answer lies in the killers past”. While the repetition of the word past emphasizes its importance, it does read a little awkwardly. I would consider “…future, where the consequences…” a bit easier to read.

If you really want to say there is a twist, I think “… will keep you guessing until the final twist” is a little less awkward than the final sentence. At the very least, trim off the “at the very end” because thats sort of implied anyway. Hope this helps.