The following version of this book was used to create the guide: Garner, Alan. Treacle Walker. HarperCollins, 2021.

Alan Garner's novel Treacle Walker is written from the third person point of view and in the past tense. The novel traces the story of a boy named Joe, and his adventures with a peddler named Treacle Walker, a bog man named Thin Amren, and a series of characters from the comic book Knockout. The novel is set in an indistinct location, and adheres to a largely linear mode of storytelling.

One day, while Joe was lying on his mattress in his three-roomed house, he heard someone calling out in the street. When he jumped off of his mattress and looked out the window, he saw a peddler with his cart and pony in the yard. Desperate to make a trade, Joe ran downstairs with a pair of dirty pajamas and a lamb's shoulder bone he had found.

Although the peddler, Treacle Walker, was skeptical of Joe's stinky pajamas, he agreed to make a trade. Joe chose a small bottle of powder from Treacle Walker's chest of knickknacks. Afterwards, Treacle Walker gave Joe a donkey stone, which he told him he could use to make magical things happen.

Because Joe had a lazy eye, he could not spend too much time in the sun. He invited Treacle Walker to join him inside his house. When Treacle Walker asked Joe about his eye patch, Joe explained that he was supposed to wear it over his good eye in order to strengthen his weak eye. The patch did not, however, seem to be working.

One day, Joe was lying on his bed, reading comics, and playing marbles against himself. When he became engrossed in his new installment of Knockout, he was shocked when the characters leaped off the pages of the book and into his room. He watched them jump into the mirror. When he told Treacle Walker what had happened, Treacle Walker guessed that he had stoned the mirror, or rubbed the donkey stone on the glass. Joe tried to break the mirror in order to get inside and rescue his favorite comic book hero from the villains, but the glass would not break. However, once he stoned the mirror, he was yanked through the glass and into an alternate world. This world looked just like Joe's world, except in reverse. When he could not find the characters, he returned to his own house.

Meanwhile, Joe was becoming increasingly frustrated with his eyes. After a particularly frustrating visit to the eye doctor, he was worried that his way of seeing was wrong. He told Treacle Walker about what the doctor had said, and conveyed his frustrations to a new friend named Thin Amren. Thin Amren lived in the bog near Big Meadow. Thin Amren spent most of his time sleeping and dreaming, but enjoyed talking to Joe when he visited. Both Thin Amren and Treacle Walker encouraged Joe to take heart. Neither of them thought there was anything wrong with his eyes.

Despite his new friends' encouragement, Joe was tired of all his dreaming and imagining. He closed his comic book characters back into their book and the mirror world. Once he told Treacle Walker what he had done, Treacle Walker led him down to the bog. He then summoned Thin Amren. Because Thin Amren's existence was reliant upon the existence of Joe's imagination, he told Joe to kill him with the tree branches he had collected. Joe made the decision to follow Thin Amren's instructions though he knew the consequences. After Thin Amren died, he mourned.

Treacle Walker and Joe returned to the house together. They talked and told jokes near the chimney. Treacle Walker comforted Joe, assuring him that he was not dead, but had simply entered a new version of life.