The Secret of the Old Attic

A boy from Zagreb, named Miro, and a boy from Prague, named Pepík, become acquainted via amateur radio broadcasting. Then, they meet in person during their holidays at the Croatian island of Hvar, to where Miro has invited Pepík. Pepík is captivated by Miro's stories about his great-grandfather, Kružić, a sea captain, scientist and inventor. The two boys get into an attic where the great-grandfather's things are stored. Here, they discover a canon with a double-sided barrel. The description translated from German by Miro's sister Božena informs them that it is an anti-gravitational canon which, if electrically charged, can lift up any object and catapult it into outer space. The boys repair the canon, lift a cart of a local carrier into the air and let it disappear. When some boxes of fish, belonging to the local fisherman, Šime, also disappear in the same way, rumours start to spread about "miracles", and not only at Hvar. Journalists keep arriving in the small town and also the boss of a local criminal organization, who is interested in the matter. He seizes the invention during a big traditional feast. But the boys as well as Božena try to protect the invention and the criminals take them to their boat. Božena, however, manages to direct the canon towards outer space and catapults both the criminals and the ship. The children jump into the sea just in time. They are saved by the police but nevertheless say nothing to anybody about the invention. The mystery of the old attic is preserved and the children can now enjoy their summer holidays in peace.