When Brandon Stivers and his family move into his dead grandmother's river house for the summer, he is immediately drawn to the swampy area at the river's edge. Susceptible due to his autism, it doesn't take long before Brandon succumbs to the call of the dark spirits that reside there. He begins to offer small sacrifices to the muck in exchange for the euphoric feelings he's never experienced, but when he meets a neighborhood girl named Amy, his summer takes a deadly turn. When Amy begins talking about tossing an obnoxious neighbor into the muck to cure her mother's cancer, Brandon must decide how far he will go. He wants to please the girl he's falling in love with, but he also knows that the muck gives, and the muck takes away.