If you’re familiar with the true story on which “The Impossible” is based, you’ll know a little about the finale. In case you don’t, I’m not going to spoil this real-life disaster movie about the effects of the 2004 Pacific tsunami on a family of five. And when I say “disaster movie,” I’m not speaking about big-budget spectacles. This is a serious film about the effects of a disaster on one family.

The family includes Henry (Ewan McGregor), his wife Maria (Naomi Watts), and their sons Lucas (Tom Holland), Simon (Oaklee Pendergast) and Thomas (Samuel Joslin). They are spending Christmas at a resort in Thailand when the disaster strikes on Dec. 26.

When the tsunami hits, the audience is taken by the same surprise as the family members. In an instant, they are flung far apart. Maria manages to reconnect with Lucas, 12, and they literally cling to each other as they face the devastation wrought by the disaster and the fear that they may never see the rest of the family again.

Henry remains with Simon and Thomas, struggling to find hope as he seeks the whereabouts of his wife and other son.

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Maria is gravely injured in the floodwaters. Right away, we see that she is losing blood because of a leg wound, and we watch as she relies more and more on her son simply to keep moving and find shelter. Mostly, we watch as the two make their way toward what they hope will be safety. Less and less, we hear them talk, and it becomes evident that Maria’s life is ebbing away.

Although the focus is on a family, we never forget that these characters represent the all-too-true plight of those affected by such a ghastly event: Many people never saw their loved ones again after the tsunami, and the fear portrayed by all of the main characters, as well as some of the people they meet, is palpable and convincing. There’s a bit of contrivance toward the end, but that doesn’t mean the movie as a whole is not worthwhile.

You won’t see a bad moment of acting here. Although Watts and McGregor are wonderful, the children are particularly compelling. It is a story of how ordinary people react when faced with tragedy. If you appreciate real-life stories being brought to the big screen by capable performers (think “127 Hours” and “Into the Wild”), you will appreciate this.