Lucas, along with parents Maria and Henry and two younger brothers Thomas and Simon go on a family vacation to Khao Lak, Thailand. Lucas is shown to be very obnoxious at first, seeing his younger brother feeling scared on the flight, claiming nothing scares him. Once arriving on Christmas Eve, Lucas and his family settle in and begin enjoying the resort they were staying at. On Boxing Day, however, a massive tsunami approaches the resort. Lucas and his mother Maria eventually emerge from the swirling water and find one another, with Maria having sustained serious injuries to her leg and chest. They help a young boy, Daniel, from the wreckage and are soon found by locals who transfer them to a local hospital in the city of Takua Pa. Daniel is separated from them during the journey. At the hospital, Maria encourages Lucas to help others find their family members while she goes into surgery for her chest injuries.
While Maria was in surgery, her medical chart was mixed-up with another patient who had died. Lucas eventually returns to find his mother's bed empty and is then taken to a tent where children without families are kept safe. The mistake is discovered when Lucas cannot identify any of the dead woman's jewellery and he is subsequently reunited with his mother who has been moved to a private room in the ICU. She had the name "Muriel Barnes" written on her arm. In the hospital while he waits, Lucas finds Daniel and sees that he has been reunited with his father.
From a distance, Lucas recognises his father and while searching him out in the chaotic crowd outside, Lucas' siblings spot him and they reunite. Lucas's father Henry heard their shouts and finds the three of them together. He learns that Maria is in the hospital ready to undergo more surgery for her leg, which she later survives. Flashbacks reveal how she came to be badly injured and how she surfaced the water. While in surgery, Lucas tells his father he has something really important to tell Maria.
The following day, the family boards an ambulance airplane to Singapore so Maria may receive further medical treatment, arranged by their insurance company. On the plane, Lucas tells his mother he knows Daniel is safe. 
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