Ten-year-old Kaatje yearns for her older brother Karel's approval, but he acts like the boss treating Kaatje as if she's careless and incompetent. Karel has all the adventures too, going on sailing trips and entering races with his sailboat. When Kaatje gets left behind on the way home from a school trip, she falls into a canal and gets fished out by a boy living on a canal barge. This leads to new friendships and exciting trips on the barge with his family.