The following version of the novel was used in the creation of this study guide: Rowling, J.K. The Christmas Pig. Scholastic Inc. 2021. Hardcover.

The novel begins with a very young Jack and his beloved toy pig, Dur Pig (or DP for short). As Jack grows up, he and DP do everything together as Jack sees DP as a living toy with wants and emotions. However, just after Jack starts attending school, his parents separate and Jack is forced to move with his mum 100 miles away near his Gran and Grandpa. While this upsets Jack, he does not tell his parents and thinks that DP is the only one who understands him.

At Jack's new school, he befriends an older student named Holly, a gymnast with dreams of going to the Olympics. The two become close over the course of a year, but things change when Holly's mother leaves her father and Holly has to choose between them. Eventually, Jack's mum marries Brendan who is revealed to be Holly's father and Holly begins to bully Jack, telling him that Brendan is not his father. As a year goes by, Jack becomes very angry with Holly, but again keeps his thoughts to himself.

On Christmas Eve, however, Holly runs from her mother who is upset that Holly lost a recent gymnastics competition. This frustrates Jack, especially when Holly mocks his toilet paper angel and knocks the tree over, causing the family dog to destroy it. Gran and Grandpa take Jack and Holly to replace the Angel, but Jack is so upset with Holly that he calls her a loser to bother her. Holly snaps and throws DP out of the car window and, when Grandpa cannot find it, Jack goes ballistic, as DP is the only security he had left. Even when Holly and Grandma return with a replacement called the Christmas Pig, Jack is so angry that he attempts to rip the Christmas Pig's head off until they leave him alone.

That night, as Jack plans to go looking for DP himself, various Things around his room come to life and the Christmas Pig tells Jack they can save DP from the Land of the Lost if Jack promises to return the Christmas Pig to Holly once they return. Jack agrees and the two fall into the Land of the Lost after being chased around the house by the dog.

After a temporary stay in Mislaid, Jack and the Christmas Pig are sent to Disposable: a city for Things that are easily replaced. From there, they learn that the vicious ruler of the land called the Loser is looking for Things that do not belong. They manage to sneak to the city of Bother-It's-Gone inside Lunchy the Lunch Box, but are forced to hide again when the Loser's Loss Adjusters begin searching the town. They are saved by the Things Poem and Pretense who help them escape to the Unlamented Wastes where unwanted Things - also known as Surplus - are sent to be eaten by the Loser.

With the help of a Surplus named compass, Jack and the Christmas Pig meet an abandoned Blue Bunny and Jack's replacement angel that fell into the tree after it was knocked over again. Together, they travel across the Wastes until they are confronted by the Bad Habits. This includes Bullyboss, a representation of Holly's jealousy towards Jack as it is revealed that she felt he was stealing her dad away from her and that she wishes to pursue music instead of gymnastics. Everyone is forced to flee as the Loser arrives, but the broken angel and some of the Bad Habits are taken.

Jack, the Christmas Pig, and Blue Bunny travel to the City of the Missed where Blue Bunny acts as a decoy so they can sneak inside. Suddenly, Blue Bunny is found by a girl in the Up Above after being lost in a bush for weeks and is pulled out of the Land of the Lost.

In the City of the Missed, Jack and the Christmas Pig are helped by a glowing woman named Happiness before they are taken to the palace. Once there, they meet King Power and the other leaders including Ambition, Principles, and Memory. Power announces that he knows Jack is a young boy and that he can turn him and the Christmas Pig over to the Loser for more control in the Land of the Lost. Happiness and Hope arrive in time to help Jack and the Christmas Pig escape when Power tries to overturn the vote to protect them and seize the Loser's favor for himself.

Hope takes Jack and the Christmas Pig to the Island of the Beloved where destroyed Things that humans greatly care for end up. There, Jack meets DP and Toilet Paper Angel, but is dismayed to learn that the Christmas Pig decided to sacrifice himself so that DP can return to the Land of the Living in his body. With the help of DP and Santa, Jack travels back to the Wastes and enters the Loser's lair to save the Christmas Pig. The Loser almost eats him, but Jack instills hope in the captured Things to open a pathway back to the Up Above where they can be recycled into something new.

Then, Jack wakes up under the Christmas Tree with the Christmas Pig who he now calls CP. He forgives Holly and encourages her to start guitar lessons when Brendan gives her one for Christmas. In the end, Jack is grateful for the Christmas Pig and promises to love him as much as he does DP. The Christmas Pig cries in happiness as the novel ends.