Sally and her unnamed brother sit and stare out of a window on a cold, wet day. The children's mother is away, leaving them home alone and bored. After a loud and sudden thump, the Cat—a tall, flamboyantly dressed, anthropomorphic cat—enters the house, greets the children, and offers them to show them some fun games and tricks. While the Cat claims that the children's mother would not mind his visit, the children are silent, unsure of how to respond to the Cat's offer without their mother present. The children's pet fish suddenly leaps from his bowl and urges Sally and the boy to force the Cat to leave: "He should not be here/When your mother is out!" (52-53).
The Cat shows Sally and the boy his first trick: an elaborate balancing act involving several household items. With the fishbowl propped on top of the umbrella, the Cat stands on a ball while holding a book, a glass of milk, a toy ship, a fan, and a cake. He begs for the children’s attention so they can learn how to have fun, though he soon loses his balance and falls, and all the items topple to the floor. Livid at the mess, the fish demands that the Cat leave.
Instead, the Cat brings in a big box and unleashes Thing 1 and Thing 2, two identical creatures with poofy blue hair and matching red jumpsuits. After shaking the children’s hands, the Things recklessly fly kites inside the house, knocking down most of the household belongings. Angered by the mess, the boy declares, "I do NOT like the way that they play/If Mother could see this,/Oh, what would she say!" (223-225).
Suddenly, the fish spots the children’s mother walking toward the house's front door, which prompts the boy to track down and capture the Things with a net. With newfound confidence, the boy demands and successfully gets the Cat to leave. Then, the fish, Sally, and the boy start panicking—though the Cat and the Things are gone, the house is still in a state of complete disarray and chaos. The fish frets that they will not have enough time to clean the house before their mother's return, but the Cat abruptly returns with a vehicle that swiftly cleans, dusts, and puts back all of the items in their original place. The Cat bids his final farewell.
Relieved and overjoyed at the restored house, Sally and the boy return to their chairs by the window. Back in the house, the children’s mother asks how they spent their day and whether they had fun. The children do not know how to respond, leaving the boy—also the book's narrator—to pose a question to the audience: "Now what SHOULD we do?/Well.../What would YOU do/If your mother asked YOU?" (306-307).
