context: As the story opens, it is too rainy and cold to play outside, so a girl and a boy sit bored and look out the window. Their mother announces her departure, tells them to have fun, and says she'll return at 3:30 sharp. While their mother is out on a shopping errand, they're left to wish for something to do.
  The mysterious, quirky Cat in the Hat suddenly enters with a bump and fools around a bit. The family goldfish named "Karlos K. Krinklebine", demands that he must leave, but the Cat instead plays a game which he calls "Up, Up, Up, With a Fish", placing the fishbowl on top of a stack of bubbles. The girl notices that the Cat is making the house a little dirty, and the boy recalls their mother's projected return at 3:30. Noting their objections, the Cat bows to the voice of the majority and dejectedly states he's going to Siberia. Immediately after leaving, however, the Cat bursts back in claiming that his "moss-covered three-handled family gredunza" has been stolen. The Cat accuses Mr. Krinklebein of being the thief, and sings a ballad about the loss of his treasured keepsake.
  The Cat then leads the kids on a search for the missing gredunza using his method of "Calculatus Eliminatus," drawing random numbers and letters anywhere the gredunza isn't to mark that they've already checked there. This makes a mess of everything, Mr. Krinkelbein once again demands that the Cat leave. Ostensibly to gain sympathy, the Cat sings a pessimistic song to convey his low self-esteem, then puts Mr. Krinklebein to sleep by singing a lullaby. Having made a miraculous recovery from his bout of depression, the Cat brings out Thing One and Thing Two to aid in the search for the gredunza, singing to the kids that they can find "anything under the sun." Instead of being productive, however, the Things play a variety of sports using Mr. Krinkelbein's fishbowl, noting that every house they visit has a pessimistic fish. Mr. Krinkelbein becomes angry and accuses the Cat of not being a real cat ("Whoever heard of a six foot cat?!"), and his hat of not being a real hat. The Cat is indignant, and asserts his legitimacy by singing his name in several languages, real and fictional. The song becomes so catchy that everyone, even Mr. Krinkelbein, joins in and contributes. (An interesting point to note is that in the Russian portion of the song, the Cat describes himself as a "chapka in a shlyapa", which translates to "Hat in a hat," not "Cat in a hat.")
  As the song ends, Mr. Krinklebein spots the mother coming home. The Cat exits, leaving behind an extremely messy house. He quickly returns, however, using a motorized vehicle to tidy things up. He departs for good, hinting that he may return someday, and the mother returns. She asks the kids how their day was, and tells them that she just saw a cat in a hat "going down the street with a moss-covered three-handled family gredunza". While the exact identity of the item is never revealed, this indicates that the gredunza was never really lost, and the Cat simply wanted an excuse to have more fun. The boy and the girl look out the window much as they did at the beginning of the special, and watch as the Cat walks off to his next adventure.
question: Why must the house be perfectly clean?
answer: upcoming meet and greet for work with mother's germaphobic boss.