The Friend is written as a sort of meditation, with a stream-of-consciousness, deeply interior narrative addressing events as its unnamed narrator sees them. These events are interspersed with contemplation on a variety of subjects—such as suicide, writing, and pets—and groups of people, such as victims of sexual assault, the narrator’s peers and students in the worlds of writing and academia, and pet owners. The novel is somewhat encyclopedic, referencing thoughts and musings from a variety of famous figures, most particularly writers.

The book opens with a meditation on abuse and the suffering of women, from Cambodian refugees to victims of sex trafficking; this is revealed to be the final subject that the narrator and her friend discussed through email before his death by suicide. The book is primarily written in the first person, and it is directed toward the narrator’s friend in much the same way as a letter. The narrator frequently pauses to address her deceased friend directly, simply referring to him as “you.”

The narrator attends her friend’s memorial service in a state of removed shock and contemplates the events leading up to “you’s” suicide. She reveals that “you” had been married three times, and all three wives are present at the service. The third wife, who was married to “you” at the time of his death and is simply referred to by the narrator as Wife Three, requests a meeting with the narrator, much to her dread. Wife Three reveals to the narrator that—against her wishes—her late husband had adopted a dog, an enormous Great Dane that he had found abandoned in a park.

Though Wife Three had attempted to convince her husband to give the dog to someone else, “you” had eventually worn her down. Over the course of these arguments, however, “you” had repeatedly brought up the narrator as an option, saying that she “lives alone, doesn’t have a partner or any kids or pets, works mostly from home, and she loves animals.” Worn down by her grief and by Wife Three’s seeming lack of other options, the narrator decides to take the dog, Apollo.

The narrator’s building has a strict no-dogs policy, but the narrator cannot stand (or afford) to lose her apartment, as it is one of the rare rent-controlled apartments in Manhattan. She makes no effort, however, to be covert about the presence of Apollo. Her super, Hector, is apologetic but firm, stating that if the dog is not removed, he will have to contact the landlord in Florida.

With no recourse, but flat-out refusing to part ways with Apollo, the narrator begins “waiting for a miracle” and finds that those close to her are becoming concerned for her mental health. Many believe that she is ascribing some sort of metaphysical significance to the dog. Indeed, the narrator admits on more than one occasion that Apollo seems to her like an extension of her friend—and that taking care of Apollo and ensuring that he is loved is, for several different reasons, something that she has to do.

Time passes, and the main narrative becomes interspersed with the narrator’s musings on the literary industry and the viability of writing as a career. She makes half-hearted attempts to appeal to her super and eventually her landlord, who cannot be reached. She receives three warnings about getting rid of Apollo, with each warning threatening eviction proceedings more blatantly than the last. Still, she is frozen in her refusal to get rid of Apollo. At one point, “Wife Two” offers to take Apollo, but the narrator refuses out of fear that Wife Two is planning something sinister.

In the wake of this behavior, the narrator’s friends begin to lose contact with her. As she drifts further into solitude, she begins spending all of her time with Apollo. Those who are still in contact suggest—and even insist—that the narrator should seek therapy. In therapy, the narrator is finally forced to attempt to articulate her grief, all of which has been drastically underplayed up to this point. The therapist believes that the narrator has been in love with “you” for a long time and is thus mourning “as a lover would. As a wife would.” With the help of her therapist, the narrator is able to register Apollo as an emotional support companion, and her landlord finally concedes that she and Apollo can stay in the apartment building.

Soon after, the narrator realizes that “one miracle is not enough”: though she and Apollo are able to continue living in her apartment, the narrator begins to consider that Apollo will certainly die before she does. She worries about Apollo’s advancing age, noting that gray hairs appear on his muzzle, his eyes are red, and his arthritis is becoming worse.

At the beginning of part 11, the narrative style shifts after the narrator wonders,

How should the story end? For some time now I have imagined it ending like this.

The writing is no longer directed at “you”; instead, it is spoken in the third person about an unnamed woman (who is presumed to be an imagined version of the narrator). The woman starts her day and takes flowers to a convalescing friend. It is revealed that her friend has survived a suicide attempt, and though he is embarrassed, he is happy to be alive. He recounts his time on the psych ward and a loose poetry workshop that he participated in while he was there. He thanks the woman for looking after his dog during his recovery. The woman reveals that she has been writing a book based on her friend’s story, operating under the fictionalized assumption that he had not survived his suicide attempt. This book is revealed to be the chapters of The Friend up to this point, with the woman taking out or changing the names of the characters and changing the dog’s name from “Jip” to “Apollo.” The precise nature of this story, such as whether or not it is based in reality or even true within the narrative, is not revealed.

The book’s final part once again returns to the point of view of the original narrator; however, she no longer addresses her old friend. Instead, she speaks directly to Apollo, confirming that he was close to the end of his life after all. For one last summer, she has relocated to a summer house on Long Island while her apartment is cleaned. Though everyone at her apartment building loved Apollo, the smell and mess that his aging body generated became too much even for the narrator, and it became increasingly difficult for Apollo to get around the city. The narrator is largely at peace, but she muses about the cruelty of time and wishes that Apollo could stay with her forever. Apollo is no longer a mere stand-in for her friend: he is his own being, and she ends the book by lamenting the coming death of her companion:

I want to call your name, but the word dies in my throat.
Oh, my friend, my friend!