Amused by the comment that it began as a rough-out for a possible TV series. I can actually see how that would work. Substantially changed along the way? I do believe it: two of your four main characters are black, and one of those-- the most normal of the lot-- is gay as well. Good work.
It has however wiped out any memory I had of that Pinborough horror/ mystery that I read in January. My mind has room for only one set of police inspectors with crumbling marriages handling horrific murders in London; I can no longer even recall Who Did It, or why.