On Midsummer's Eve, 1974, Annie Raft arrives with her daughter Mia in the remote Swedish village of Blackwater to join her lover Dan on a nearby commune. On her journey through the deep forest, she sumbles upon the site of a grisly double murder--a crime that will remain unsolved for nearly twenty years, until the day Annie sees her grown daughter in the arms of one man she glimpsed in the forest that eerie midsummer night.