Colin the Crab, the most skillful builder on the eastern riverbank, never hesitates to help his friends. Now Colin is busy with his own new project-a garden pavilion for his home. But after a week of hard work, the pavilion of his dreams is still unfinished. Even worse, a boisterous fish family has taken over the construction site. The exhausted Colin buries himself under a blanket and refuses to open his curtains. Puzzled, Colin's friends call an emergency meeting-it's time for them to take action!

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Klaus Krabbe, den dygtigste håndværker på den østlige flodbred, tænker aldrig to gange, før han hjælper sine venner. Efter en uges hårdt arbejde, står det blå lysthus, han har drømt om at få bygget sig i haven, stadig ufærdigt, og en højrøstet fiskefamilie har invaderet hans byggeplads.

Klaus, som er helt udmattet, gemmer sig under dynen og nægter at trække gardinerne fra. Klaus' venner undrer sig. De indkalder til hastemøde. Det er på tide, vennerne tager affære.