This film is based on a true story that happened during the 2004 Indian Ocean tsunami. Maria (Naomi Watts) and Henry (Ewan McGregor) took their three sons to Thailand to spend Christmas together. Unexpectedly, the day after Christmas, when this happy family was enjoying a leisure time by the swimming pool, a huge wave of thousands of feet like a beast came towards them. Maria, who was shocked by the scene in front of her, was unable to react for a while and was unfortunately swept away by the huge wave; and although Henry caught her two sons in time and prepared to escape, it was still too late, and the fierce flood finally washed them away. Maria, who was once knocked unconscious by the huge wave, woke up and found herself floating on the sea, and all the scenery around her was submerged under the water. She was convinced that her family had all died, but she found that her eldest son Lucas was floating on the sea just a few meters away from her. Maria was suddenly given a shot of adrenaline, and she decided to do everything she could to leave alive with her eldest son Lucas...