2.5, rounded down for the ridiculous premise. Demons, really? HUH? I thought Gerritsen was a doctor? Was I wrong to assume this implied she was a somewhat rational thinker who believes in science, evidence, and the whole range of human emotions and behaviors (vs. believing that evil people are the spawn of the Nephilim/Devil?)... Um.... No, just NO. I've liked some of the others in the Rizzoli & Isles series, but this one just comes out of NOWHERE, and pulls us into an absurd tale of the occult, evil incarnate, ancient conspiracies, haunted houses, secret societies... Too much suspension of disbelief is required to truly enjoy The Mephisto Club.