The devotion of suspect X

I'm not the biggest fan of crime fiction, and picked this up in a charity shop but it's brilliant!

"Sometimes, all you had to do was exist in order to be someone’s savior."

I was having doubts about this half-way through. The math teacher's character is the thing being questioned the whole time. He certainly is a very interesting character and we get this in the very first pages, with more being revealed as the novel progresses. We see one thing, then the author reveals something that completely upsets what we have thought so far. Sticking with this until the end was a good decision. The title is very apt.

This book changes the premise of the traditional "whodunit" to a "howdunit". Excellent, and some of the twists are particularly effective.