Stanley Potts is just an ordinary boy, but when all the jobs in Fish Quay disappear his Uncle Ernie develops an extraordinary fascination with canning fish. Suddenly their home is filled with the sound of changing machinery and the stench of mackerel, and Uncle Ernie's obsession reaches such heights that he would even can Stan's beloved goldfish! Stan, however, has his own destiny, which leads him – via a hook-a-duck stall – to Pancho Pirelli, the blue-caped madman who swims with piranhas. And as Stan delves into the waters, he finally discovers who he really can be.