"Bedevilled" follows a woman named Hae-won, who decides to travel to the island of Mudu in order to visit her childhood friend Bok-nam. We learn that Bok-nam is living in an abusive household, and that the only thing that keeps her going is her love for her daughter, Yeon-hee. When Bok-nam begins to suspect that her husband, Man-jong, is sexually abusing Yeon-hee, she begs Hae-won for help. Hae-won refuses to get involved, forcing Bok-nam to try to escape on her own with Yeon-hee.
Bok-nam gets caught by her husband, who tries to punish her. Yeon-hee intervene and is accidentally killed by Man-jong, who pins Yeon-hee's death on his wife. Bok-nam snaps and sets out to kill everyone on the island — including Hae-won, whom she blames for Yeon-hee's death.
