Lammas Night by Katherine Kurtz

Never judge a book from its trashy-ass cover. This one shines inside. The story is about a bunch of magick-users, wiccans, witches, neopagans using magic to keep Hitler from invading Britain in 1940. The point is, the author presents all these occult practices so logically, so believably, such a down-to-earth way that I almost started to doubt if it this kind of stuff may even really work. For a non-fiction work that would be considered a dark art, but for a fiction work, it is just being truly excellent at creating a suspension of disbelief.

Highly recommended for Eliezer as it can give ideas for HPMOR.