Two young radio amateurs, Miro from Zagreb and Pepek from Prague, spend summer holidays on the island of Hvar, in Miro’s aunt’s house. In a dusty attic of her old house they find a strange gun made by Miro’s great-grandfather, a crazy inventor. They discover that this is in fact an anti-gravity gun taking gravity away from objects and launching them into outer space. The boys set up the gun and start launching things in the air, causing a stir. An international spy organisation is trying to get their hands on the powerful weapon. An entertaining sci-fi for children, whose original score was composed by Arsen Dedić, a great singer-songwriter for children and adults.