When renowned botanist Dr. Rosa Marquez receives a strange sample from the secluded and mysterious Hemlock Isle, her instincts tell her that something is amiss. Following the recommendation of an old colleague, she invites the investigators to join her on a survey of the island. Nothing could prepare them for what they find: deadly, mutated wildlife and a strange, malignant presence permeate the isle, all while the local residents prepare for a festival, seemingly unaware of the danger. The investigators only have three days to find out what lurks beneath Hemlock Vale before its people meet a terrible fate.