A group of children on the Adriatic island of Trs, led by newcomer Karlo, discover a lost African boy, Chiku, at the lighthouse. As they try to help him return home, local boy Bumbar opposes Karlo's unusual pseudo-scientific experiments. During a heated argument, Bumbar hits Karlo, losing the trust of the group. However, he redeems himself by helping to expose a smuggler trafficking children from Africa to the European Union, who tries to take Chiku away from them. The summer adventure concludes with the capture of the smuggler, bringing the group closer together.