Lock Every Door

Lock Every Door by Riley Sager gets 4 stars from me!
The premise was interesting, but of course too good to be true.
The building made me think of The Dakota or H.H. Holmes' murder castle.
We get to know the protagonist Jules' backstory at a good pace, bit by bit as the plot starts to move along.
I did have a good theory fairly early on, I was pretty much right about it. I
The bit where Jules does research and concludes through the symbols that they're a satanic cult was kinda lame, I would have been so disappointed if that was the case. It would have felt like a cop out and felt a lot like Rosemary's Baby. The actual truth was more interesting and unique. I wasn't quite satisfied with the ending though.
I loved his other book Home Before Dark, but his other books seem so different, this one isn't really that much of a horror, to be honest. It's still a pretty good thriller!