"Kaew" rushes back to her hometown in the provinces immediately after receiving news that Koi (her younger sister) is possessed by a ghost, simultaneously with several other students. This resembles an event that happened to herself and her friends when they were children. Kaew tries to find a way to cure Koi with the help of Dr. Danai, who identifies the symptoms as "mass hysteria," which conflicts with the beliefs of the villagers who are still superstitious. The events of Kaew's past begin to return to haunt her again after she had tried to escape them for a long time. At that moment, Kaew meets a close childhood friend who has become a teacher at her sister's school. She is the one who holds various secrets that will help unravel the mystery of a boy who disappeared in the past. When what they did together in childhood unexpectedly results in consequences in the present...