Milo, Tock, and the Humbug are happily working away on the absurd projects they were assigned by the faceless gentleman when Milo points out that he feels like he could go on forever. He decides to use the magic wand the Mathemagician gave him to figure out just how long it will take him to complete his task and discovers that it will be 837 years. Milo confronts the gentleman and discovers that he is the Terrible Trivium, "demon of petty tasks and worthless jobs, ogre of wasted effort, monster of habit."
The travelers run away from the demon, running and scrambling up the increasingly steep and difficult path with the Trivium not far behind them. From nowhere a voice begins shouting what seems to be helpful advice, directing the three companions through a confusing part of the trail. But before they know it, they drop into a deep pit and realize they've been tricked. The owner of the voice introduces himself as the long-nosed, green-eyed, curly-haired, wide- mouthed, thick-necked, broad-shouldered, round-bodied, short-armed, bowlegged, big-footed Monster—or simply the Demon of Insincerity.
The demon warns Milo and his friends not to try to escape from the pit since he is "one of the most frightening fiends in this whole wild wilderness". Tock and the Humbug cower in fear, but Milo pulls out the telescope that Alec Bings told him would show things as they really were. He takes a good look at the Demon of Insincerity and discovers that he is a small, pathetic-looking animal. Crushed by Milo's realization of the truth, the demon wanders away while the travelers climb out of the pit.
They continue along the path for a time and, upon stopping for a rest, find themselves in the palm of the Gelatinous Giant. They do not notice the giant until he announces himself because this demon tries as hard as it can to look exactly like whatever is around it. Being different simply is not safe, the giant explains. Milo cannot believe that someone so big could be afraid of anything, yet the Gelatinous Giant says he is afraid of everything, especially ideas. Milo pulls out the box of words that King Azaz gave him and shoos the giant away with it.
And so the travelers are on their way once again. News of their journey seems to have spread across the demon network, though, and soon an entire throng of monsters is hot on their trail. Once they spot this horrible crowd, among its members all of the demons they had already met, Milo, Tock, and the Humbug press ahead at an even more urgent pace.
Racing ahead, the three companions soon come upon the staircase to the Castle in the Air. As they reach the first step, they notice a little man at a desk with a huge book upon it. The Senses Taker asks all sorts of questions about the travelers that become increasingly trivial, and he writes down all of the answers in his ledger. They become engrossed in the question game and forget all about the castle and the horde of demons chasing them until Milo drops the bag of sounds that the Soundkeeper gave him. The package breaks open and explodes with laughter, pulling Milo from his trance since humor is the one sense the Senses Taker cannot seize.