David comes to the popular island camp Prelestje for a vacation like every year with his grandmother. But this year everything is different. He is now a teenager and is very bored without any real company. Grandma tries to make him friends with the older Alja, but David is not interested in it at all. He can't wait for his cousin to come to the camp so that some action can begin. Then he sees a zombie behind the tent. Or maybe the green night lights of a sailboat? Suddenly, boredom is no longer a problem! He and his friend are almost run over by a black SUV, a strange creature visits him in the tent, a stranger appears who stepped on a poisonous fish - a lot of suspicious things start happening. It's a good thing that there are smart and brave friends here who take matters into their own hands and solve the criminal mystery. (summarized from the main page of mladinska-knjiga.si)