When archaeologist Fiona Scott (Saffron Burrows) uncovers an ancient burial casket on a remote Irish island, she unwittingly awakens a dark force that has been imprisoned for centuries. Drawn to the mysterious relic, her daughter Lily (Emily Flain) breaks the seal and unleashes The Morrigan, a vengeful pagan war goddess whose return sparks a wave of terror across the isolated community. As a violent storm cuts the island off from the mainland and the body count rises, Fiona must race against time to save her daughter from possession and stop an ancient evil before it escapes beyond the island's shores.