Genesis sees couple Koldo and Clara about to celebrate the most important day of their lives: their wedding. Everything appears to be running smoothly and the bride and groom and their families are enjoying a wonderful day; that is until some of the guests start showing signs of a strange illness. Before they know what's happening, the bride and groom find themselves in the middle of a hellish ordeal, as an uncontrollable torrent of violence is unleashed on the wedding. Amidst the chaos, Koldo and Clara become separated and begin a desperate search for one another. What started off as an idyllic day quickly descends into a nightmare of the worst kind...
