Suddenly in the Dark is a story about Kang Yu-jin, a wealthy biology professor conducting a butterfly field study, who hires a new housemaid named Mi-ok. Mi-ok is the daughter of a shaman priestess who recently died in a house fire.
At first, Yu-jin and his wife, Seon-hee, welcome Mi-ok into their home. However, Seon-hee becomes suspicious when she sees a strange wooden doll that the maid has brought with her. Seon-hee has been plagued by nightmares about the same doll and starts to believe that Mi-ok is trying to kill her and take over her household.
In a moment of madness, Seon-hee causes Mi-ok to fall to her death. After this tragic event, Seon-hee is haunted by visions of the doll attacking her, leading to a spiral of torment and fear.