A conman named Geonho marries Jihye, a naive single mother, determined to wring her dry. The same day he moves into her house, he comes face to face with her only son, Jinsoo — a shut in who never leaves his room. After Jihye leaves for work, the door to Jinsoo's room creaks open... Geonho, who Jinsoo won't acknowledge as his father, gets dragged into the room — and trapped inside.