Isaac and his Mother live a simple, happy life in a small house on a hill. Everything changes when his Mother begins hearing a voice from above claiming to be God demanding proof of her devotion. To save her son from sin, she strips Isaac of his clothes, locks him in his room, and eventually moves to sacrifice him. In a desperate bid to escape his approaching mother, Isaac finds a hidden trapdoor under his bedroom rug and plunges into the dark, monster-infested basement below.