Oh, how the sun laughs from the sky! Actually a perfect washing day - but the little elderflower-white church mouse Tilda Apfelkern would rather enjoy the beautiful weather together with Rupert. Unfortunately, he's not in a good mood at all: there's a problem with his sea urchin collection! Fortunately, Tilda knows right away how and where to solve this problem - on the beach! And so they set off on an adventure where some secrets await the two friends ...