Help me identify a fantasy novel

I read a novel in the late 70s/early 80s (may have been written earlier, but it seemed contemporary) with the conceit that magic was an ordinary part of everyday modern life. I don’t recall the details of how this was worked out, but my memory is that it was suburbs, cars, contemporary America, plus magic. The main character was a werewolf, and the one detail I remember well is that he had an invisibility cloak called a Tarnkappe.

The plot revolved around some kind of secret war in the Catholic Church, which was a dominant institution and pro-magic. I don’t remember the theology of it, but in this world the church had been shaped mostly by the teachings of John (which John? I dunno) and not Peter. The “Petrine” faction, which was also against magic, was trying to take over.

Any ideas?

This is “Operation Chaos” by Poul Anderson - great book.

https://en.wikipedia.org/wiki/Operation_Chaos_(novel)

Thanks AndyL! The cover shown on the Wiki page is the one I remember, too.

Happy to help. I didn’t like the sequel “Operation Luna” nearly as well, but your mileage may vary.

Grin! Mileage always varies! I liked Operation Luna more than Op. Chaos; I thought it was a bit more sophisticated and mature, and better developed.

(And the guest appearance by Fu Manchu – Fu Ch’ing! – was lovely! One of the best Fu Manchu novels ever!)

I agree that Luna wasn’t as good.

For the OP’s benefit, both are a “serial-numbers filed off” loving homage to Heinlein’s “Magic, Inc.” (which I can’t recommend highly enough)