Classes used will be Pistolero, Shaman, Oracle and Ninja-ish.
Setting it late 1924.
Trick is, magic doesn't really exist for normal folk, and no one wants them knowing. So no flashy spells. Keep it on the down low otherwise it will draw the attention of people with really BIG guns.
Ghouls (CR1) have an intelligence of 13, you think they don't know about guns and possibly explosives? :D
Cultists of course have access to the same spells, same guns and less moral qualms about blowing away innocent seeming by-standers. Again this will be as much or more about role as roll. Considering the way most adventures end in D&D, trying to do it quietly is more of a challenge than any CR I could otherwise dream up.
And there is always the napping Shoggoth under Arkham if things get too out of hand.