During a time when they are sensitive to death, mourning the loss of the family mother, Gerry and Jessica have to endure a completely separate occurrence of death. They realize that there is an astonishing connection between their dead wife and mother, Donna, and the dead bodies that turn out to be missing victims. Donna encountered them while they were alive, and then mysteriously, they died and were entombed in their freezer, and Donna has died of cancer, so there is no summoning her to help solve the mystery.
That is what the novel is literally about, but of course a plot as symbolic and synchronous as this is begging to be analyzed further. By continuing to think more about the plot, the reader might discover that there is essentially an elaboration of mystery here. Instead of gradually discovering the answer to the riddle of death, the reader (and Jessica, the protagonist) are pulled into the unfathomable strangeness of death. Because of a dual experience of death, she is even more apt for this encounter with death.
Her two points of view on death are the familiar and strange. When they find dead bodies in a freezer, that is a cold experience. It does not arouse deep agony the way the death of a warm mother would. The cold bodies are more like objects. They are evidence in a more scientific, detached experience of death that helps provide a counterbalance for the reckoning of perception that occurs with the death of a parent. The death of a parent is symbolized as a loss of information, because Donna would be able to explain everything about the dead bodies if she had not also died herself. The number three (two strangers and a friend) is symbolic because it points toward the universality of death.