Mexican folklore melds with J-horror elements and the brooding atmospherics of Spanish horror specialist Jaume Balaguero in director Rigoberto Castaneda's loose adaptation of the La Llorona legend - a frightening tale that has been passed down from parent to child for generations. Agata and Catalina Hameran are twin siblings whose already powerful bond was infinitely intensified when their mother suffered an unusually traumatic death. It was on that day that the sisters discovered they have the power to communicate telepathically, regardless of the physical distance between them. One night, when Agata is badly injured in an accident on the 31st kilometer of a dark road that runs alongside the forests of Mexico City, Catalina experiences an overwhelming wave of dread. While Agata was rendered comatose in the accident, Catalina continues to hear her sister cry out in agony from some alternate plane of reality and realizes that something is horribly wrong. Compelled to explore the history of this lonely stretch of road after a series of bizarre supernatural occurrences, Catalina soon finds out that Agata wasn't the first person to suffer tragedy at the 31st kilometer marker, and vows to uncover the connecting factor between this strange series of seemingly unrelated accidents.