Summer is for trashy beach novels and Dennis Wheatley's 1934 The Devil Rides Out definitely qualifies. We discuss problematic genre fiction, fake rituals, the rhetorical trap of being asked "do you believe in evil?" and racial demonology of the late British empire.
Some useful scholarship: Timothy Jones, "The Black Mass as Play: Dennis Wheatley's The Devil Rides Out" M/C Journal, 17(4).