From publisher blurb:
Angels and devils are one and the same—beings beyond our comprehension from a place called the Empyrean. Heaven, hell, demons, those are base attempts at classifying the unknowable by limited mortal minds. Instead of fearing them, you should learn from them, and use their power. Just like the Order of the Mercyful Sepulcher.
This is a system neutral sourcebook that helps inject a mixture of divine and occult into your games. With statistics for D&D (5e or old-school) and Hypertellurians, but useable in any adventure game system.
10 powerful occult tomes, each with descriptions, rumors, and 1 or more orphic spells or rituals
Tools of the trade, including the Tactical Ordnance Mobile Battle Shrine, Hallowed Hand Grenades, and Bad Habits
Adventure seeds throughout the tomes, and in their own section
4 character concepts to play battle nuns (and their porter) of the Order