Showing Something Wicked this Way Comes by Ray Bradbury

It's the week before Hallowe'en, and Cooger and Dark's Pandemonium Shadow Show has come to Green Town, Illinois. The siren song of the calliope entices all with promises of youth regained and dreams fulfilled . . .
And as two boys trembling on the brink of manhood set out to explore the mysteries of the dark carnival's smoke, mazes and mirrors, they will also discover the true price of innermost wishes . . .