Kenichi is painting a model ship, when Yumeko turns up, wearing a woolen jumper over her usual clothing. A freak accident causes paint to get splattered over the jumper, and Yumeko, not very pleased, asks Hattori to wash it. Hattori complies, and the paint is washed off - but the jumper shrinks! Yumeko is distraught, but goes home anyway.
Meanwhile, Hattori and the gang are planning on what to do, when Tsubame turns up abruptly. After listening to their problems, Tsubame offers to make another jumper. She knits. And she knits. And she knits some more.
The following morning, Hattori, Tsubame, Kenichi, Shishimaru and Shinzo are still in the attic, all having fallen asleep over the jumper. They wake up suddenly and realise that the jumper is too big! Then Shinzo comes up with an idea - wash it. They do so, and the jumper is reduced from large to normal.