This book describes an idea me and Mr Monroe talked about concerning deities in the Southern Reaches. The premise is that the Fey never really retreated from the realm but took on a new role is disguise. That of deities, who once were absentee landlords in the lives of mortals. Through religion and cults they could grow in power through their followers and sew discord between Light, Balance, and Shadow. The alien Fey feed on chaos and, after the mortals of the world banned together against the Fey, the Lord of the Mists came up with a brilliant scheme.
The book allows Chroniclers to create entire pantheons or single deity for their campaign, showing how their characteristics and other statistics might be represented. This is not a Deities & Demi-Gods conversion.
There is also a section describing a possible new magic system for your campaign. Divine Magic is based loosely on Deep Magic from the excellent book Advanced Sorcery and other Divine Magic mechanics from other systems somewhat compatible with this one. I should point out that while I and my players enjoy variety in magic, the system MW already has in place is perfectly fine as is without this supplement. Sometimes easier is better.