Martha, Mats and Mikkel really had other plans for their summer holidays. But when mum has an accident while on business in New York, and Dad goes to be by her side, who will look after the three kids? Well, they will have to go to Sommerby to stay with their Grandmother, where then have never been before.
What at first sight looks like really bad news, will turn into the most wonderful summer the three siblings ever had. Quickly they get used to the slightly gruff Grandmother and begin to enjoy the completely different and utterly free life on the country side, close to the sea.
But when Grandmother suffers from acute back pain and is unable to move, she is dependent on the children’s help. Help which puts them into grave danger.
The little sailing boat in which they sail to the other side of the bay to get the shopping done, gets into heavy waters, and a thunderstorm very nearly capsizes the boat. Luckily they get rescued at the very last moment. When the holidays are over and mum returns, everybody has not only learned a great deal but all of them have moved a lot closer together.