Disclaimer, I couldn't write a book and am in awe of those who can.
This is a clever story line but the writing style is remarkably difficult to follow. Introspective italicised paragraphs. sometimes in first person, sometimes in third, interrupt the narrative and add little to its flow. Stephen King was the first author that I encountered using a similar technique but he seemed almost to weave a parallel story - this didn't. Overly descriptive parts, followed by unlinked elements - a lake house, a ravine, a boat, a water patrol, all appear without warning. Good people become bad, bad become good without adding much. Revenge sex, not sex, not suicides; all rather confusing and rather nugatory. The language and word order often grated: a couple of times I checked the writer's bio in case the book had been written in another language (French perhaps) and translated to English, but from what I glean the writer is a native English speaker.
So I enjoyed the plot, and was utterly distracted by the other challenges.