Didn't solve part A, solved part B probably to the same degree as other readers did and I thought that I'm about to rate it as 3 stars because A wasn't too interesting and I probably could figure it out.

The author played with the dangling plot lines really well, again, though. That said...

...as the book was reaching the conclusion it, to quote @johnathan arnold, started getting better and better. All the buildup was well worth it!

Above maximum for detective fiction, easily.