A grieving mother, Hee-yeon, moves with her family to the countryside to find peace after the disappearance of her son. They settle near a mysterious mountain known for its ominous folklore involving a legendary tiger spirit that mimics human voices to lure people. One day, Hee-yeon discovers a lost girl in the woods who eerily resembles her missing child. She takes the girl in, hoping to learn more about her son’s fate, but strange occurrences begin to plague the family, leading Hee-yeon to question the true identity of the child and delve deeper into the mountain’s dark history.

As eerie events unfold, Hee-yeon's husband and mother-in-law also become entwined in the mystery. The family dog goes missing, and they hear unsettling sounds mimicking their voices. Fearing for her daughter's safety, Hee-yeon battles her skepticism and desperation as she seeks help from local villagers familiar with the ancient tales. Tension rises, and the line between reality and legend blurs, driving Hee-yeon closer to a terrifying revelation that forces her to confront the malevolent presence threatening her family’s survival.