Nicknamed 'the little thunderbolt', Astrid loves to spend her days racing down the hillside on her sledge or skies. But poor Astrid longs for other children to come to her village and join her adventures. Instead, she has to put up with a grumpy 74-year-old for a best friend (although secretly she wouldn't have it any other way). Astrid's world is about to be turned upside down, however, first by the arrival of a strange family, and then a mystery woman. Her best friend, Gunnvald, has been keeping a secret from her - one that will test their friendship to its limits. Everything is changing in Astrid's valley, and she's not sure she likes it.