One day, Plop receives a letter from his grandfather, Kabouter Knap, stating that he is very ill. The only thing that can save him is the juice of the carob root. Before the hourglass is emptied, Grandpa Knap can be saved but there is one big problem: Plops grandfather lives on the other side of the gnome forest. Together with Plop's friends, they build a large balloon, so that they fly to Knap in time. Plop stops the juice of the carob root in a basket of puff cakes to keep it safe. But because Plop is so tired, he sinks down on a chair and falls asleep. The next morning, Smul is extremely hungry and, without realizing it, takes the basket with the plop cakes. Plop does not notice this, because he is still sleeping next to the basket of puff cakes. When Smal starts looking for Smul, the hot air balloon rises, with Plop, Klus, Kwebbel and Lui in it. There starts a dangerous journey..