I finally found something that gives me the same feeling as Sager's Home Before Dark (which I know was actually published after Lock Every Door, but I read HBD first), which is one of my favourite mysteries ever.

I really loved this story. The vibes are just immaculate. Amazing creepy building, weird residents, suspicious rules and an even more suspicious history. I love that I had no idea whether it was paranormal or human activity. I loved all the hints and being able to piece the story together. I think I've started to prefer stories that read like puzzles, not ones that give you a ton of red herrings just to surprise you at the end. And it was great to see characters who weren't just complete idiots making decisions that just aren't believable.