A group of friends on vacation decide to venture onto a trail high up in the mountains that has been closed for repairs. The climb proves more perilous than planned, especially as they soon realize that they are not alone. The adventure turns into a nightmare.

In December 2004, close-knit family Maria, Henry and their three sons begin their winter vacation in Thailand. But the day after Christmas, the idyllic holiday turns into an incomprehensible nightmare when a terrifying roar rises from the depths of the sea, followed by a wall of black water that devours everything in its path. Though Maria and her family face their darkest hour, unexpected displays of kindness and courage ameliorate their terror.