Do you enjoy the Pathfinder system? I'm assuming you do.
Would you like a way to run an encounter, a session or even a campaign centered around a mystery without frustrating your players when they can't roll well enough to beat your DCs?
This is the book for you.
GUMSHOE allows you to run a mystery the right way -- not by limiting access to clues, but by providing easy access to clues and making the interpretation of those clues into the mystery.
It's not a long book, but it is definitely high quality.
The pdf is definitely worth adding to your arsenal.
So I should come clean and say I was the judge that selected this for the Judge's Spotlight ENnie.
Edge contains a very inspiring setting. It is fantasy, but set in a world with only humans. There are otherworldly beings that humans call angels and devils, but they aren't quite as we on earth use those terms.
The culture of the world is filled with opportunity for adventures and plot hooks.
And if you enjoy this book, I recommend checking out Remnants, which is a sci-fi RPG also from Outrider Studios. It's also a high quality product.