Sabine, a young girl in rural Louisiana, is concerned and enraged when her alcoholic widower father, Dempsey, misses an Ash Wednesday church service. To save him, and their small family, Sabine pushes Dempsey to give up drinking for Lent. However, keeping sober proves more challenging than Dempsey had anticipated. He breaks his vow, evoking the wrath of the Rougarou, a mythical bayou beast that punishes bad Catholics. To save her father, Sabine must go into the bayou to defeat the beast. Her attempts quickly go awry, and Dempsey must step up as a parent and come to the rescue -- but the dangers in the swamp are just the beginning. To truly defeat the Rougarou, Sabine and Dempsey must confront their fears and come together as a family.