Na samom dne Chyornogo morya zhivyot groznyy osminog Shprut. On derzhit v strahe vseh morskih obitateley. A eschyo… on pytaetsya zavladet tainstvennoy Zhemchuzhinoy. Tolko otvazhnyy delfinyonok Denik i ego vernyy drug - morskoy konyok Plastik, gotovy protivostoyat zlodeyu i sohranit mir v morskom tsarstve. No osminog Shprut okazyvaetsya silnee samih delfinov - hraniteley volshebnoy Zhemchuzhiny… Eta istoriya o druzhbe, vzaimopomoschi, o vernosti seme, ob otvage i priklyucheniyah, kotorye pomogut malenkim chitatelyam ponyat, chto dobro vsegda pobedit!
