The following version of this book was used to create the guide: Lin, Chia-Chia. The Unpassing. eBook ed., Farrar, Straux and Giroux, 2019.

At the beginning of the novel, Gavin, the book’s ten-year-old protagonist, has three siblings: Ruby, a toddler; Natty, who is starting kindergarten, and Pei-Pei, his teenage sister.

The family immigrated to the U.S. a few years before the beginning of the novel, moving to Michigan first and then to Alaska, where the majority of the novel is set. They live in a small house in a secluded neighborhood about 40 minutes from Anchorage, Alaska, surrounded by a forest that the children love to play in. There is only one neighboring family, the Dolans, and even they are quite distant.

Gavin contracts meningitis at school. He is feverish, and spends days drifting in and out of sleep. During this time, Ruby contracts the illness from Gavin and dies. While ill, Gavin sees the family slowly get rid of her things, and by the time Gavin recovers, there are almost no remaining signs of her existence in the house.

Over the first half of the novel, tension builds between the family’s parents, especially on the mother’s side. She does all the cleaning, cooking, and shopping, and starts lashing out at her husband when the family's financial situation starts to deteriorate. The children attempt to both recover from the loss of their sister and maintain peace within the family. During this time, Gavin finds out that his father is being sued by a family who blames him for their son's illness. His father built a well which was not sufficiently sealed, resulting in the family's son falling ill due to the toxins in the water.

The novel's climax occurs in Chapter 11, when Pei-Pei serves as their father's makeshift lawyer due to her relative proficiency in English and accompanies him to the hearing with the other family. There, the father signs a document agreeing to pay a settlement to the family. When they return, the mother berates the father for bringing misfortune down on the family. That evening, Gavin and his father go for a drive. Gavin finds Ruby's urn is in the glove compartment, and finds out that the father wanted her ashes to be spread in the water near their home. Gavin and his father leave the car to look at the ocean, but are almost trapped in the silt mudflats. In a moment of frustration with his father, Gavin pours Ruby's ashes into the mud to trap her there.

Eventually, the financial strain of the court case becomes too much for the family. They are evicted, and go on a short trip down the coast while living in their truck. After a short couple of weeks, they return to the house and move back in, largely using the wood stove and candles for light in order to keep the house looking empty.

The father barely lives at home, often going out to work odd jobs. Pei-Pei, meanwhile, sneaks out at night to spend time with Collin, the neighbor boy whom she is dating. One day, Gavin, Natty, Pei-Pei, Collin, and Collin's younger sister (and Gavin's friend) Ada are spending time together in the forest. After an argument, Natty goes off alone, Pei-Pei follows Collin, and Gavin returns home alone. As night falls and Pei-Pei comes home, they realize that Natty has not returned. Pei-Pei and Gavin go out to look for him in the forest, but Pei-Pei becomes hypothermic. The Dolan father comes by the house and takes Pei-Pei to the hospital.

Natty returns home eventually, but the stress of the night results in an intense argument between the mother and father. The mother blames the father for Ruby’s death, the family’s financial misfortune, and for Pei-Pei’s hospitalization. She tells him to leave for good and, overnight, he does.

An unspecified amount of time later, Ada comes to their front door to give Gavin an envelope of cash. The Dolans had purchased a lottery ticket on behalf of Gavin's family – and it won. Gavin’s mother chooses to use the money to move them to Seattle, a more diverse city where the family don’t stand out as much. The last two chapters of the novel function as a sort of epilogue, following the remainder of Gavin's childhood. As he grows older, he searches for places where he might feel that he belongs, even going back to the Taiwanese fishing village where his mother grew up, but finds he is unable to fit in anywhere. The novel concludes with Gavin recalling a time when he cut his mother's hair shortly before her death, which reminds him of playing with Ruby as a child.