During one of his shore excursions in Caputh, navy captain Achim Hartung inadvertently gets into trouble with the law. To please his long-time friend Hauke, he drives him to a small nearby island in a motorboat. A check by the water police reveals that Captain Hartung is not in possession of the required "Binnen" recreational boating licence. Since Achim defiantly refuses to pay the ticket, he is sentenced to community service at the local swimming pool. Within four weeks, he must successfully complete the adult swimming course to "Seepferdchen". Otherwise he faces prison.
