The following version of this book was used to create the guide: Nagamatsu, Sequoia. How High We Go in the Dark. HarperCollins, 2022.

Sequoia Nagamatsu’s How High We Go in the Dark is written from the first, second, and third person points of view, and employs both the past and present tenses. The novel embraces an atypical narrative structure, which disrupts conventional notions of time and space. The following summary adheres to the author's chapter divisions, while relying upon a linear structure and the present tense.

In "30,000 Years Beneath a Eulogy," after Cliff's daughter Clara dies while performing environmental research in Russia, Cliff travels to Siberia to complete her work. When he arrives, the research team tells him about Clara's discovery of the Ice Age girl's remains in a nearby cavern. Cliff's evolving relationships with the team and growing investment in Clara's research, gradually alter how he sees himself, his life, and the world beyond. He finds it increasingly difficult to engage with his wife Miki and his granddaughter Yumi when they call him. Eventually, a mysterious virus seeps out of the Ice Age girl's body and infects the crew. Cliff realizes they will not survive.

In "City of Laughter," after the Arctic plague outbreak, Skip has trouble finding work as a stand-up comedian. He accepts a job at a new euthanasia park called The City of Laughter. The park is designed to help children die peacefully and to help their parents say goodbye. When Skip meets Dorrie and her son Fitch, his relationship with his work changes.

In "Through the Garden of Memory," shortly after contracting the plague, Jun falls into a coma. While in his comatose state, Jun travels into a memory garden. He meets many people, all of whom are caught between life and death. Together, the companions journey in and out of each other's memories, allowing them to understand one another better. When a woman has a baby, Jun and the others deliver them out of the darkness and back into life.

In "Pig Son," Dorrie's ex-husband David is a research scientist who harvests organs inside pigs' bodies. The organs are then used to save children dying from the plague. David has devoted himself to this work ever since Fitch's death. He is shocked, however, when one of the pigs starts talking. David soon establishes a relationship with the pig that teaches him about fatherhood and family.

In "Elegy Hotel," Dennis works as a bereavement coordinator at an elegy hotel. The hotels are places where families visit their loved ones' bodies before the bodies are cremated. Dennis likes the work because it grants him a sense of purpose and anonymity. When his brother Bryan asks him to come home and care for their dying mother full time, Dennis's illusory realm feels compromised. He avoids talking to Bryan and fails to say goodbye to their mother before her death.

In "Speak, Fetch, Say I Love You," a husband struggles to grieve his late wife, Ayano. Ever since Ayano's passing, his relationship with his son has been difficult. Eventually the father and son learn to mourn Ayano via their connection with their robo-dog, Hollywood.

In "Songs of Your Decay," Aubrey researches the cadavers of plague victims at the plague ward where she works. Her life changes when one of her research subjects, Laird, arrives at the ward alive. Laird is volunteering his body to science knowing that he will soon die. In the weeks before his death, he and Aubrey grow close. Aubrey struggles to reconcile with his death in the weeks after his passing.

In "Life Around the Event Horizon," not long after Bryan's wife and daughter die from the plague, he remarries a woman named Theresa. This rapid marriage upsets his son, Peter, and fractures their relationship. Bryan is also preoccupied with his scientific research. Most recently, he has had a black hole planted in his brain, believing the singularity might grant him insight into the future. Though he knows the singularity will kill him, he thinks it is his only chance to save his family.

In "A Gallery a Century, a Cry a Millennium," six years after the plague's outbreak, Miki and Yumi board the U.S.S. Yamato. Because life is rapidly dying out on Earth, they hope to find a new planet to call home. While traveling through space and time, Miki paints the spaceship walls with memories from Earth, hoping to preserve some remnant of the past for future generations.

In "The Used-To-Be Party," Dan Paul writes a letter inviting his neighbors to reconnect. His experiences during the pandemic have taught him the importance of forming relationships with others.

In "Melancholy Nights in a Tokyo Virtual Cafe," Akira's life has not been the same since the outbreak of the plague. The pandemic kept him from finishing his degree and finding stable work. In the narrative present, he spends most of his time in a virtual representation of Tokyo. It is here that he meets a single mother named Yoshiko. This relationship teaches Akira about the importance of family and friendship.

In "Before You Melt Into the Sea," the narrator works for a company Eden Ice, which offers alternatives to burial and cremation. He falls in love with one of his clients, Mabel, and struggles to say goodbye when she dies.

In "Grave Friends," Rina travels back to her hometown in Niigata City, Japan after years away. Almost as soon as she arrives, she feels overwhelmed by guilt for abandoning her family. Her grandmother's memorial and her revelation regarding her pregnancy make her reflect upon the past and hope for the future.

In "The Scope of Possibility," Theresa has lived her whole life traveling through time and space. Throughout her travels, she has kept her daughter in her heart and her seed farm in her mind. Both represent hope to Theresa. She longs to be reunited with her daughter someday, and believes that with the farm, she can grow new futures.