AllMovie

In this animated film based on the cartoon characters of Marten Toonder (the characters have been around since 1939) a mysterious egg gets tossed into a peaceful town during a storm and "Swellbelly" emerges. Swellbelly comes from the other side of the Black Mountain and when upset, he has the ability to assume any enormous size he wants -- a feat that only Ollie the Bear can keep under control. It seems that the newborn Swellbelly has bonded to Ollie like he would to his mother. Then some nasty business happens in the town when Ollie is accused of a bank robbery -- but Tom the sharp and wily Cat has the talent to resolve that sticky wicket -- and while he does so, Tom is working out a plan to finally unite Swellbelly and his distant and undoubtedly worried mother.