Milo is a boy who does not know what to do with himself. He is bored senseless by practically everything in his life and is constantly trying to find something exciting or interesting. Milo especially dislikes his schoolwork because he cannot understand the use behind learning geography or math and thinks that learning is "the greatest waste of time of all."
One day, Milo goes into his bedroom to find a strange package waiting for him. The box is not quite square but not quite round and is addressed to "MILO, WHO HAS PLENTY OF TIME." There is no return address on the package, and Milo has no idea who might have sent it to him—it is not his birthday or Christmas. Deciding that there is no way he can return the box, he opens it. Inside he finds an unassembled turnpike tollbooth, a map, a book of traffic rules, and an instruction manual. He puts the tollbooth together and gets into a small electric car, one of the many toys he is usually too bored to play with. As he approaches the tollbooth he is told to have his destination in mind, so he randomly picks the city of Dictionopolis from the map and passes through the turnstile.
Once through the tollbooth, Milo finds himself speeding along a country highway. He is shocked to discover that the tollbooth was no toy at all. Since it is a beautiful day on the road, he continues on his trip. Before long, he arrives at Expectations where an excitable little man rushes up to his car. The Whether Man, has a habit of saying everything three times. In response to Milo's questions about how to reach Dictionopolis, the Whether Man talks nonstop about navigation and the weather.
Milo presses on, leaving Expectations. The road gets increasingly curvy and repetitive. Bored by the seemingly endless circles, Milo's mind begins to wander and he becomes very drowsy. The car also seems to tire and grinds to a halt. As he sits, almost asleep, a distant voice informs Milo that he is in the Doldrums.
After looking around, Milo realizes there is a tiny man sitting on his shoulder who changes color to match it. He then notices a number of little people around him hiding like chameleons. They introduce themselves as the Lethargians and describe their idle lives in the Doldrums, explaining that thinking and laughing are both outlawed.
Suddenly a large dog with a clock for a body comes running up, frightening the Lethargians away. The watchdog whose job it is to make sure nobody wastes time, suspiciously asks Milo what he is doing in the Doldrums. When Milo replies that he is "just killing time," the watchdog becomes furious and tells Milo that the only thing worse than wasting time is killing it. He tells Milo that if he wants to leave the Doldrums he only needs to do the opposite of what got him there. Since Milo drifted into the Doldrums by not thinking, he concentrates on thinking and his car begins moving. Soon he is back on his way to Dictionopolis with the watchdog.