Magos and Joseph moved from Mexico City to Joseph’s family’s estate of Firgesan in Upstate New York in the hope that the fresh air would be better for Santiago’s health. There was a dogwood tree in front of the house that fascinated Magos. All winter, she poured hot water over the tree, fearing it would die in the cold. Santigo died before the dogwood’s first spring flowers emerged. Magos believes the first bloom is her son reincarnated, but then considers the “cruel” and “ridiculous” trick of Santiago coming back “as something so ephemeral, frail, and beautiful” (12), and she kills the blossom.

Santiago’s body is cremated, and Magos and Joseph spread his ashes at the base of the dogwood tree, where Santiago would sometimes sit to draw monsters. In the aftermath of his death, the couple “haunts” one another. Magos follows her husband around the house, observing his grief. She can’t remember speaking, eating, sleeping, or showering.

Joseph calls Magos “a demon” and demands that she stop following him. He tries to talk about their shared grief and what they should do next, if they should stay in New York or move back to Mexico, but Magos does not engage. Sometimes Joseph becomes angry, and they fight, but his anger dies more quickly than Magos would like. Magos watches Joseph begin to “decay” and become “boring.” She wants to see him “break,” but instead he merely “withers.”

Magos leaves her husband and returns to Mexico City.

Magos doesn’t remember buying a plane ticket, packing, or arranging a ride, but her best friend, Lena, is there to pick her up at the airport and take her to her mother’s house.

Magos’s mother, Lucía, her housekeeper, Jackie, and her dog, Almendra, greet Magos at her childhood home. Lucía laments that she learned about Santiago’s death from Lena; Magos hadn’t told her. Magos is surprised. Santiago feels “so [hers]” that it didn’t occur to her that her mother was also experiencing a loss. She laughs, and her mother sends her up to her room for rest.

As Jackie helps Magos unpack, she finds the chunk of Santiago’s lung. She tells Magos an old story about a woman who fed a dead girl’s heart until it grew into a beautiful man who fell in love with her. They had a child together, but then the man and woman were both murdered, and their baby disappeared. Magos believes Jackie’s story, but she also doesn’t believe the same thing will happen to her. She knows that the “lump of flesh” in the jar is not her son (24), but Jackie still advises her not to feed the lung.

Unable to sleep that night, Magos pours some chicken broth over the lung. She feels “silly,” but also figures the experiment is harmless. Back in her room, she looks at a crack in the wall, remembering the powerful earthquake they survived when Santiago was young. She and Joseph lived in the neighborhood of la Roma, and in the aftermath of the quake, Magos carried Santiago all the way to her mother’s house while Joseph stayed to help the neighbors. On the way, Santiago had an attack, gasping for air on the sidewalk. Passersby gathered, but Magos would let no one help; “Santiago’s lung was [hers] to conquer” (29), and she was soon able to calm his breathing.

The next morning, Magos is shocked to see that the lung has consumed the chicken broth. She is eager to feed it more, but Jackie and Lucía are already awake. Downstairs, Lucía tells Magos that she wants to have a mass for Santiago. Magos is against the idea, but Lucía insists. She tells Magos it is important to “acknowledge” the loss and share their grief. She also insists that Joseph should be there, and Magos reluctantly agrees to call him.

Santiago was born with just one “underdeveloped” lung. The doctors told them that he wouldn’t make it home from the hospital. Only Lena, then a medical student, was sure that Santiago would live. As he grew up, Santiago vacillated between being a happy, active boy and being incapacitated by his weak lung. Afraid of coming home to his son dead, Joseph began working from home, and Magos dedicated herself to making their lives happy. She organized family plays, in which she was the protagonist, Joseph the villain or lover, and Santiago the secondary characters, often wearing monster costumes he created himself.

Magos calls Joseph to tell him about the scheduled mass. He asks Magos why she cut open Santiago’s body, and she tells him she took a piece of his lung. Joseph wants to know what the lung is like. He accuses Magos of having “no heart,” but agrees to think about coming to the mass.

Neither Joseph nor Magos is religious, but Santiago had been fascinated by God until he announced at dinner one night that God “hadn’t chosen [them]” to care for (40).

After mass, the bereaved gather at Lucía’s house. Magos hates the guests’ pitying eyes and gentle voices, so she hides upstairs and watches the gathering from above. Lena comes to sit with her, and together they watch one of Magos’s cousins sobbing dramatically, “performing the grieving mother” (42) until Lucía puts a stop to it.

Suddenly, Lena is surprised by a small, scuttling creature she takes to be a mouse. Magos realizes it is the lung. She fishes the hissing creature out from under a closet and rushes into her room. She shoves it into a shoe box and tells a confused Lena that she threw the mouse out the window. Lena notices that Magos’s finger is bleeding. She is concerned that the “mouse” gave Magos rabies, and Magos shows her the lung to ease her worry. Lena is not convinced. She insists that the creature, which has become rounder and grown a “protuberance” resembling an arm or a tail, is a “misshapen rodent” that should be put out of its misery.

The lung grows on its preferred diet of beef and pork. Dark fur grows over its body, and two eyes appear above its wide mouth of sharp fangs. Its awkwardly placed “arm-tail” sprouts a paw with three sharp claws, and the lung uses it to hang from Magos’s closet rod to sleep.

Jackie constantly pesters Magos about the state of her room, offering to clean it for her, but Magos is focused on keeping the lung secret. She urges Jackie, who has worked for Lucía for 20 years, to take a day off and go out.

Twice a week, Lena comes for dinner, and Magos tries to appear “chirpier,” showering and dressing nicely. Lena brings Magos gifts and avoids speaking of Santiago.

Magos suspects that her mother is struggling to make ends meet with her retirement pension, but Lucía refuses her offer to help. She also refuses to consider selling the family home and moving into a smaller apartment. She urges Magos to put her attention on repairing her relationship with Joseph instead of worrying about the house.

That night, Magos is awakened by a commotion downstairs. The dog, Almendra, is on the patio, wild with fear, with the lung’s teeth sunk into her flank. Jackie is shrieking and trying to beat the creature off with a broom. Magos wrestles the broom away from Jackie and attempts to separate the lung from the dog’s leg. She squeezes the creature until it is forced to let go. Magos feels compelled to apologize on behalf of the lung and express her “disgust” for it, but she knows the sentiment would be “insincere”: The lung just attacked the dog because it was hungry and didn’t know any better.

Magos cradles the lung while Jackie cleans Almendra’s wounds. Jackie insists that Magos cannot keep the “dangerous” lung. Magos, however, refuses, promising that she will “teach it to behave” (58). Jackie is skeptical, but agrees to keep the lung a secret from Lucía for one more week.

The next day, Jackie barely speaks to Magos. Lucía wonders what happened between them and quizzes Magos on what she plans to do next. She asks her daughter if she misses Joseph and tells her that Lena is in love with her. Magos knows about Lena’s love, but doesn’t like her mother exposing this “secret treasure.” Magos and Lena lived together during university, and once shared a “delicious kiss full of saliva and desire” (65), but Magos “didn’t lust” after Lena the same way she did.

The next day, Lucía leaves Magos a new notebook with a note telling her to “[w]rite [her]self a new role” (67). Magos calls Joseph. She asks him to return to Mexico City, telling him that she has something of Santiago’s to show him. Lured by this promise, Joseph agrees.

Joseph arrives later in the week, looking “gaunt” but also clean. He carries only a small bag and insists that he will stay in a hotel rather than in Lucía’s house. Lena arrives, and Lucía insists they “celebrate” with tequila. Joseph and Lena were also friends in university, before Magos and Joseph got together, and they spend the evening reminiscing happily. Magos feels “whole.”

Lena stays over in the guest room, and Joseph insists on sleeping on the family room’s sofa bed. That night, Magos sneaks downstairs and climbs into bed with Joseph. She tells her husband she missed him, but he tells her he “stopped missing [her] a while ago” (74). He tells her that he expected his body to “gnarl” with grief, as his Uncle’s had after his mother died. Instead, he became terrified of his loneliness and then angry with Magos for leaving. These two emotions helped him to continue living. He is still angry with Magos and doesn’t know if their relationship can continue.

Reluctantly, Magos takes Joseph upstairs to show him the lung. The creature is hanging upside down in Magos’s closet, and Joseph mistakes it for a possum. Joseph begins to cry as Magos explains what happened with the lung, then looks at her with “unbelievable pity.” She tells him they can move back into their house in la Roma and become a family of three again. He begins to laugh, then cries more. He tells her that he thought that she “didn’t care” when Santiago died, but now he sees her looking “terrible,” and he understands that she is more of a “mess” than he is. In the middle of their argument, Joseph realizes that the lung is no longer in the closet. He and Magos are searching for it when they hear Lucía scream.

Magos and Joseph rush into Lucía’s bedroom to find the lung latched onto her thigh. Magos hurries to her mother and attempts to detach the lung’s fangs without injuring it. Lena and Jackie arrive, and in the chaos, Lena calls for a hammer. Lucía thrashes on the bed, then faints. She comes to as Joseph returns with the hammer.

Lena finally drags the lung off of Lucía and holds it out to Joseph, commanding him to hit it with the hammer while Magos begs them not to hurt the creature. Joseph strikes the lung, and it falls limply to the bed. Magos rushes to the lifeless creature and begins to cry for the first time since Santiago’s death. Her family stares at her in silence, and Magos holds the lung to her chest and flees the house.

Magos takes “[her] monster” to a nearby park. She cannot summon the will to dig a grave, so she leaves the lung’s body there in a small garden. Lena finds Magos later that night. Magos doesn’t want to return to her mother’s house, so Lena drives them through the city.