Death
The primary imagery of this novel is obviously death. Death is what is shaping the world of Jessica and Gerry as they mourn the death of their respective mother and wife, and death is what they discover as the inciting incident of the novel. This makes the imagery of death basically dual in the book. There is the "cold" death, the deaths of people whom neither Jessica and Gerry know, and there is the "warm" death of the mother whose death does resonate with them, shaking them to their core. Both experiences are defined by unparalleled fear.
Life as suffering
Sometimes, life is taken for granted by a novel, but not this one. Because of the predominance of death in the novel's plot and thematic content, life is shown as imagery through contrast. As Jessica goes on living, she analyzes what life is. Simultaneously, she analyzes her father in light of the stark revelation that—horrifyingly—one's own parents are secretly mortal like the rest of the world. She also curates an investigation into the deaths of the freezer bodies, and she discovers that their lives were horrifying and full of violence and sexual abuse. That is not an encouraging discovery for her.
Family and perception
It is important to mention the imagery shift that death causes in Jessica. For the father too, as a matter of fact, because his perception of his daughter is forever changed by a new association: She naturally will remind him of his now-dead wife, which is ultimately painful, but she also shares that pain, bringing them closer. Jessica's perception of family is changed by her awareness of mortality, and also because now it isn't "Mom and Dad," whatever those words represent. Now she sees her father as "Gerry."
Discovery and mystery
The tone of the novel is shaped by the imagery of mystery and discovery. Jessica looks for insight and makes gradual discoveries on various fronts. This imagery gives the novel a genre-feel like a mystery-thriller, but the climax of the novel is actually the abrupt ending of the novel, because that is the death of the book. When the novel ends without resolution, the books main argument arises. Each person has to decide what death means: the book cannot answer the questions it raises, so it just ends, leaving the reader to mourn the book like Jessica mourns her mother.
