There are so many overly used phrases and terms I could use to describe The Ancient Ones: couldn't put it down, worthy of an award, fabulous, awesome. I would call it breathtaking.
You have Professor Peter Stevens who wants to prove the existence of the paranormal and collects Dybbuk boxes and other vessels containing spirit or demons. Then, when his world goes insane he can only think of his unscrupulous competitor as someone who could help him. He befriends many on the good side of the paranormal who can come to his aid, but is it too late?
I think this book has excellent cinematic potential, too. Anyway, I give it five stars and you will find it a bargain at $2.99, too.
The Amazon link: https://www.amazon.com/dp/B073X6VQ7Y
The Book trailer: https://www.youtube.com/watch?v=ktUam7C50nA