Lena is a gifted surgeon and stays focused through her eight-hour surgery. However, as soon as the procedure is over, she thinks of Magos and calls home. Magos doesn’t answer.

Worried, Lena rushes home, where she finds Magos up and showered for the first time. She has prepared dinner and eats with a gusto that surprises Lena. During the meal, Magos mentions the “incident” for the first time, asking Lena if she and her family hate her. Lena tells Magos that what happened wasn’t her fault, but she confesses that she knew the lung was dangerous; it had attacked Almendra before her mother, but she “didn’t care” and kept it anyway.

She tells Lena that Jackie has seen the lung alive and well, hanging from a tree near the house. Lena doesn’t believe that the lung is still alive, but she agrees to help Magos look, knowing that her friend needs the closure.

Armed with a fishing net and a shovel, Lena, Jackie, and Magos comb the neighborhood for the lung. Before long, Magos finds a pile of the lung’s poop. She follows the trail of excrement through las Lomas, and Lena thinks of how “rich and alien” (100) the neighborhood had seemed to her when she first moved in with Magos and Lucía.

Lena had been an unexpected baby, and her mother became convinced she “was a demon sent to ruin her family” (100). As a young girl, she tried to prove her mother wrong, behaving perfectly, cleaning the house, and dressing to “look like a storybook good girl” (100). However, her mother would not be dissuaded, frequently stripping her daughter naked to look for demon marks or horns and praying fervently for her salvation. Eventually, Lena realized that her mother would never see her as her daughter and began behaving like the demon she believed her to be. When she was 14, her mother tried to poison her, so her father sent her to live with an aunt. Her aunt told her she was smart, encouraged her to become a doctor, and helped her get into university. Then, her aunt died, and Lena had nowhere to go, but Magos and Lucía took her in.

Magos finally spots the monster hanging from a tree in a park, near where a group has gathered around a pair of dead cats. Magos rushes to the lung, calling out to it while Lena tells the assembled group that they are “professionals” come to take the animal away. Lena tries to swipe at the lung with the net, but it tumbles down a muddy hill. Jackie and some of the onlookers have to pull her back up.

By the time she resurfaces, the lung is safely in Magos’s arms. She tells the confused onlookers that it is a rare creature that they will take to a reserve in the northern desert. No one contradicts Magos. Jackie and Lena worry that the lung is dangerous, but Magos insists that it will grow into a boy and wants to take it back to Lena’s apartment. Lena doesn’t want the monster in her home, but she also doesn’t want Magos to leave, so she agrees.

The monster lives in Lena’s spare bedroom. She can hear it hissing and growling at night and cannot sleep. She feels “jealous” of the monster’s shamelessness and how Magos loves it “despite it being a monster” (110). One night, she goes to the monster’s room and watches it, beginning to feel “something like kinship” with the creature (110).

Magos begins calling the creature “Monstrilio,” and tells Lena that “he” likes her. They feed him raw meat, and Lena buys him a cat tower to climb on. He continues to grow larger and begins to sprout four limbs, although he continues to use his arm-tail as his primary appendage. Magos claims that Monstrilio is “developing;” he isn’t becoming Santiago, but rather growing into “something new and independent” (111). Lena becomes accustomed to having Magos in her bed, feeling the “ancient hope” that Magos will love her rekindled.

One morning, Joseph appears at Lena’s door. After Monstrilio’s attack, he traveled to Oaxaca, where he spent some time on the beach to “forget [him]self.” He doesn’t expect to see Magos there, and for a moment, Lena thinks he will scream at her. Magos informs him that Monstrilio is still alive and in the apartment. Lena worries that Joseph might snap and kill Monstrilio, and she vows not to let it happen. Upon seeing the creature, Joseph breaks into “a weird jerky laugh” (115) that turns into sobs. Monstrilio looks at him and calls him “Papi.”

Lena receives an emergency call from the hospital. She spends the afternoon with a patient, then goes to Magos and Joseph’s house in la Roma. She wonders if they will move back in with Monstrilio and be a family again. She goes into the bedroom that used to belong to Santiago, sits on his bed, and looks through one of the boy’s notebooks. It is filled with drawings of monsters, one of which looks just like Monstrilio.

Monstrilio’s vocabulary expands to include “Mami” and “Lena.” He “win[s] Joseph over” quickly (119), and he and Magos decide to move back into the house in la Roma. Lena is tasked with emptying Santiago’s room. While in the house, she sets a magazine on fire in the kitchen, scorching the floor tiles. She wants Magos and Monstrilio to continue living with her, and thinks of ways she could convince Joseph to stay in New York.

The next day, she helps Magos move in. Jackie and Lucía come over unannounced, and Lucía asks to see Monstrilio. She is shocked to learn that Monstrilio now speaks. She teaches him to say her name and tells him not to try eating her again. Watching Monstrilio in Santiago’s room, Lena starts to panic, feeling she is “about to lose something [she] wouldn’t get back” (124).

Downstairs, they eat pizza, and Lena excuses herself by inventing an early morning surgery. She heads instead to her favorite cantina, where she drinks mezcal and watches a woman drinking with work colleagues on the other side of the restaurant. The woman comes over to Lena, recognizing her as her grandfather’s doctor. Lena holds the woman’s hand too long when she offers it to shake, and she hurries back to her table.

Lena visits Magos, but only Joseph is home. He is building Monstrilio a jungle gym on the patio, complete with a little house holding his “nest” and a net over the top to keep him from escaping. Lena has been keeping herself as occupied as possible at the hospital, hoping to exhaust herself into sleeping. The woman she hired to bathe her has recently quit, and she can’t find an adequate replacement.

She watches Monstrilio and Joseph wrestle on the patio until Monstrilio wins by swinging himself onto a platform out of Joseph’s reach. Magos arrives with cans of paint, a camera and a tripod, paper, and lights. Lena helps her take them up to Santiago’s room, which Magos intends to turn into a studio. She tells Lena that she is going to become a performance artist, and takes her to the University Museum of Contemporary Art, where they see videos of a woman ripping apart books.

As they watch, Magos tells Lena that she thinks Joseph hates her, that they “taste bitter” to one another. Lena doesn’t want to talk about him, and they return to watching the performance art. Leaving the museum, they are caught in a downpour. Lena thinks that Magos is beautiful in the rain.

When a wall collapses at Lucía’s house, Magos and Joseph offer to stay over to help with the cleanup. Lena has to work at the hospital, but she agrees to feed Monstrilio so that Joseph and Magos don’t have to go home.

However, after a long day at work, Lena is so exhausted that she forgets to feed him. She rushes to la Roma as soon as she remembers. She finds Monstrilio on the patio, surrounded by the carcasses of cats, dogs, and rats. She composes herself and hurries to clean up the carnage, but Joseph returns before she can finish. Joseph goes pale when he sees what Monstrilio has done, but he helps Lena dispose of the carcasses and clean the patio of blood. Locked in his little house, Monstrilio scratches mournfully, but Joseph doesn’t let him out.

That night, a woman comes to bathe Lena. Breaking from her normal routine, Lena has sex with the woman, thinking it might help her sleep. However, she wakes at midnight and, unable to go back to sleep, calls Joseph. They meet for a drink at their favorite cantina and talk about what Monstrilio did. Magos argued that it was only natural for him to kill when he got hungry, but Joseph worries the carnage was “excessive.” Lena says it’s not Monstrilio’s fault that he is “wild,” but Joseph insists that he can learn to master his impulses.

According to Magos, Monstrilio’s arm-tail is the source of his wildness; she believes that cutting it off will help him transform into a human. This makes Lena angry; she thinks they should love Monstrilio for who and what he is. Joseph reveals that Monstrilio is speaking more, forming sentences, and even keeping track of the days with a makeshift calendar made of scratches. However, he isn’t sure how much longer he can “keep up” the illusion of a happy life with Magos. He feels like he should still be grieving his son. Lena has no advice for him.

Lena arrives on time for dinner with Joseph and Magos. Both are dressed more elegantly than Lena expected, and she feels out of place in her jeans and shirt. She immediately notices a poorly done bandage on Joseph’s forearm. Lena insists on examining the wound, the result of “an accident” with Monstrilio, and ends up giving Joseph 11 stitches.

After dinner, Magos reveals the reason for their invitation: They want Lena to amputate Monstrilio’s arm-tail. Magos is adamant that it will “help him evolve,” even as Joseph wonders if Monstrilio is “supposed to be” wild (148). Magos urges them to trust her “instinct,” which led her to feed the lung in the first place. Lena points out that they know nothing about Monstrilio’s anatomy or body chemistry; the arm-tail could contain vital organs, or healing could be impossible. She refuses to perform the surgery but agrees to conduct tests on Monstrilio to learn more about his physical makeup.

First, she has to see if Monstrilio can be safely sedated. He has no adverse reaction to the first small dose, so Lena administers a full injection. Monstrilio collapses, and Magos and Joseph are certain the creature is dead. However, Lena soon identifies something like a pulse, but she still refuses to perform the operation. She insists Magos is trying “to make him something he’s not,” but Magos tells her that she “made” Monstrilio and knows what he is (152).

Lena manages to sneak a sedated Monstrilio into the hospital for an MRI scan. Half of Monstrilio’s body has “no structure,” but the other half has “a young boy’s anatomy,” as if a child were growing inside the monster (154). Magos becomes more sure than ever that his arm-tail is “hindering Monstrilio’s transformation into his final form” (154). Eventually, Lena agrees to perform the procedure, even though she feels it is wrong.

The operation goes according to plan, and Monstrilio seems to heal well. However, as the days pass, he becomes more lethargic and despondent. Joseph is sure he is dying, while Magos believes he is preparing to “shed” his old form. Unable to face the maimed monster, Lena stops visiting.

One night, Joseph calls. He wants her help putting Monstrilio to sleep. Lena arrives with a powerful sedative, but their plan is interrupted by Magos. Lena feels “trapped in [their] family” again (157). She tells Magos that she will no longer “oblige” her and let herself be roped into her life. Magos demands that both Lena and Joseph leave the house.

After the fight, Joseph goes back to New York. Lena doesn’t hear from Magos. She struggles to focus at the hospital, drinks at her cantina, and often pays women to bathe her and have sex with her. In need of a change, Lena accepts a position as a consultant at a New York hospital and prepares to leave Mexico.

Before her departure, Lena visits Lucía and Jackie. Lucía tells her that Monstrilio is speaking more and beginning to walk upright; Magos’s “grief creature […] is becoming a boy” (161). Lucía gifts Lena two small calaverita pendants representing her and Magos to “ward off fear” (161).

In New York, Lena relishes the foreign sights and sounds. She makes plans for her new apartment, standing in the middle of the sidewalk and making disgruntled New Yorkers walk around her. While the city makes her feel small, she knows she is “not a fucking speck” (163).