Moominmamma's birthday is approaching, and Moominpappa just can't think of a suitable gift! He turns to Snork for help, because Snork is an inventor. But the hastily constructed dishwasher breaks the dishes, and the sturdy-looking homemade bicycle falls apart on its first test run. In his desperation, Moominpappa turns to the children. During their joint consultation, Moominpappa has a brilliant idea, and their joint birthday present actually surpasses anything that has come before.