Frankie is a mentally handicapped boy who more or less lives at Western Biological. His father is dead and his mother seems to be a small-time prostitute. Her clients (whom Frankie calls "uncles") either bribe or beat Frankie to keep him away. He doesn't go to school because the school refuses to allow him there. It takes him several weeks to feel comfortable enough to enter the lab; up until then, he has been watching Doc through an open door. Doc takes the boy in and gets him clothes and a haircut. He tries to let Frankie do chores and sort specimens, but his handicaps prevent him from doing things successfully. Frankie is absolutely loyal to Doc and constantly tells him that he loves him. At one of Doc's parties, Frankie makes a great success of himself by bringing a beer to a young woman; both she and Doc praise him for his consideration. The incident stays with Frankie, and, at a later party, he tries to repeat his success by bringing a large tray of beers to the guests. Unfortunately, he drops the tray on a woman. Ashamed, he hides in the basement. Doc finds him but there is little he can do to make him feel better.
The narrative shifts back to the adventures of Mack and the boys. They arrive at Lee Chong's to work on the truck. The truck has had a long career. It started out as a Model T sedan driven by a prominent doctor, who sold it to an insurance salesman who treated it badly and banged it up during his frequent drinking sprees. The next two owners converted it to a truck and removed the windshield. The last of these owners turned the truck over to Lee Chong to pay a grocery bill. Mack and the boys are all excellent mechanics, but Gay is magical with cars. He gets the truck back in shape and sends Eddie to his house to steal the doorbell batteries, with which they will start the truck. Gay warns Eddie to beware of his (Gay's) wife, who used to beat him. Eddie returns with the batteries, and the boys are off. They hang rags on the truck to conceal the fact that it has neither license plates nor a light. They have brought very little in the way of food with them, since Mack assumes they will be able to steal everything they need from farms. They make their way to the gas station, where they use Doc's note to get gasoline. They try to get a smaller amount of gas with the difference in cash, but the station owner is aware of their reputations and will give them only gas. Driving in reverse since low gear and the brakes are gone, the boys set off for the valley.
The truck breaks down midway. Gay volunteers to go back to town to get the part they need. Somehow, though, through a long chain of circumstances, he winds up in jail after a boisterous party and doesn't make it back to where the boys are camped. Finally, Eddie sets off for a nearby construction camp to steal the part from one of their trucks.
The narrative digresses to tell the story of the death of Josh Billings, a writer and humorist. He died in a hotel in Monterey and was embalmed by the town doctor, a Frenchman on the cutting edge of biological science. The day after his death a boy and his dog find some innards in a gulch behind the doctor's office, and it is discovered that the doctor has been removing the internal organs of corpses (as one would do when embalming a body) and discarding them in the gulch. He is forced to collect the organs and pay for a small coffin that will go inside the larger coffin. The town is appalled at the treatment of such a prominent literary figure.
Eddie returns with the part for the car, which he has lifted from the construction camp. The boys set off again, turning into the Carmel Valley. They run down a rooster, which will become dinner. They set up camp and begin to eat, drink, and talk. Mack is bothered by the fact that they are actually giving Doc a party to give themselves a party, but after they talk some more, they are convinced the party is a good idea. Suddenly, a man and a dog appear out of the darkness. The man owns the land they are camped on and is about to kick them off when Mack intervenes. He tells them they are collecting frogs for cancer research and then begins to flatter the man, complimenting him on his military bearing and then on his fine dog. The man warms to Mack and points out a tick bite that has lamed the dog, who has just had puppies. Mack is instantly solicitous and offers to care for the dog himself. The man, whom they have started calling "Captain," is pleased and invites them up to his house, telling them he has a pond full of frogs. Mack departs with him, telling the boys to clean up the campsite well and then follow him. Impressed by his skill at charming the man, Hazel remarks that Mack could be president of the United States if he wanted the job. One of the boys reminds Hazel that that wouldn't be any fun.
Lee Chong's Model T truck takes on a great symbolic importance in this section of the book. The truck, like Mack's plans and Mack himself, has seen several different incarnations, each successively a little more shabby. It has been modified to meet the dreams and the needs of each of its owners, and, finally, it has fallen victim to outside circumstances, in this case, an unprofitable existence and an unpaid grocery bill. The truck has come to Lee Chong in the same way as the fish-meal shack where the boys now live. The reader is left to wonder if its last owner reacted to his loss the same way the shack's owner did. At any rate, it is only appropriate that Mack and the boys, who live in the shack, get the truck. As the narrative points out, the Model T carries a great deal of cultural weight. Americans know more about its workings than about their own bodies or the planet they live on, the narrator claims. In this way the Model T is the ultimate symbol of democracy: available to all, its inner workings easily understood, able to be modified to fit a variety of needs, and a commodity of a sort that can go from the ownership of one of the town's most prominent citizens to the custody of one of its least prominent denizens. The car is also infinitely adaptable, as the boys prove by driving it in reverse when the brakes and low gear fail. Like the boys themselves, the truck is resilient, malleable, and able to change according to the situation.