The following version of this book was used to create this study guide: Lacey, Catherine. The Answers. Farrah, Straus, and Giroux, 2017.

Mary Parsons, a young woman living in New York City, finds herself broke and buried beneath an onslaught of medical bills resulting from an undiagnosed, yet debilitating illness. Hounded by aggressive bill collectors, Mary forsakes her professional and personal obligations, choosing to pursue a holistic treatment plan called Pneuma Adaptive Kinesthesia (PAKing) recommended to her by her best friend, Chandra. Despite Chandra's repeated insistence that Mary try PAKing with her specialist, Ed, the treatment is prohibitively expensive. Mary, estranged from her parents and only supporting herself by virtue of an office job at a travel agency, quickly realizes that she needs to find another means of income to afford her treatments and eventually pay off her debts. Mary scours Craigslist looking for new employment while she continues treatment, eventually applying for a position in a mysterious "income-generating experience" (9).

Throughout a lengthy interview process for the cryptic new position, Mary is slowly recovering more control over her body through her PAKing sessions, driving her desperation to continue to afford the treatment. After she is informed of her selection for the "income-generating experience" (9), her interviewer, Matheson, reveals that she will be participating in a research study with the famous actor, Kurt Sky. He is seeking to show the boundaries of human connection and investigate the true meaning of, and motivation for, love. He chooses Mary because he wants to investigate how people truly interact with him when they do not already believe they know him, and whether it is possible for him to have a genuine connection with a woman. He also wishes to understand if his relative lack of success in long-term relationships has stunted his creative growth, preventing him from completing his newest movie, The Walk. Mary slowly reveals more details of her isolated childhood, and her complete lack of pop culture knowledge makes her incredibly attractive to Kurt for her supposed purity. The experiment will parse out the various aspects of a romantic relationship, including emotional connection, sexual intimacy, and intellectual conversation. Mary is assigned to be Kurt's Emotional Girlfriend by the Research Division, the scientists leading the experiment.

As Mary begins the experiment, she questions what will eventually become of her relationship with Chandra and whether she is entering into a dangerous situation, however she ultimately chooses to continue because of her desperation to afford medical treatment. The novel switches between the perspectives of the various women involved in the Girlfriend Experiment though Mary is the main protagonist. Each woman allows the reader a brief insight into her experience with Kurt and her motivations for completing the experiment. Ashley, chosen as the Anger Girlfriend, plays the most significant role along with the lesser mentioned Intellectual Girlfriend, Maternal Girlfriend, and Intimacy Team. During her first few interactions with Kurt, Mary is taken aback by his personality and seeming inability to stop performing even in their time alone. She realizes she is, first and foremost, a prop for Kurt's own personal development and introspection rather than an active participant in any kind of relationship. In fact, as she continues to perform PAKing sessions with Ed, their relationship much more closely mirrors romantic intimacy and involvement.

Despite the structured, monitored nature of their relationship, Mary and Kurt do begin to grow closer. However, it is never truly clear to the reader whether Mary is feeling sexual desire toward Kurt, romantic motivations, or even just gratitude that his generous compensation is allowing her to continue treatment and feel truly well for the first time in many years. Kurt's feelings are typically more discernible, and he attempts to become closer to Mary because he appreciates the way that she is able to make him feel, both in control and at ease. She begins to take over the duties of the other girlfriends, entering into intellectual conversation as well as sleeping in his apartment, blurring the lines between her participation in the study for scientific purposes and her actions as dictated by Kurt's wishes.

The novel enters into the question of research and medical ethics when it is revealed that the Research Division has been pioneering new technology of Internal Directives, feelings transmitted through the sensors Kurt and the women must wear, designed to artificially create certain emotions for study purposes. Both Mary and Kurt receive these feelings, heightening their senses and awareness of each other. Despite this, they have disastrous results on some of the girlfriends, especially Ashley, the Anger Girlfriend, hired to argue with Kurt and simulate romantic discord. Although she already possesses a fiery personality, the Internal Directives begin to loosen her grip on reality and her interactions with Kurt become more potent and real to her. After this, she begins to see Mary as a threat to her own position as she begins absorbing the duties of the various girlfriends. She starts following Kurt outside of their scheduled interactions and attempting to make contact with Mary and Kurt on their dates and simulated experiences. Despite this, Kurt and Mary continue to meet at restaurants and more frequently in his apartment where they sit and Kurt talks about himself or works on his movie with Mary as a kind of background prop.

Throughout the novel, Catherine Lacey alternates between the present happenings in Mary's life, as well as connecting her past to why events in her present begin to unfold. Despite the explicit contract that Mary is not to enter into a sexual relationship with Kurt, her past recounting of a violent sexual assault while living in the city colors her fear that she will unwittingly be taken advantage of again. Additionally, she reveals the origins of her somewhat demure behavior to be a leftover remnant of her life with her father, a fiery religious man, Merle, who had hopes that Mary would be able to follow in his footsteps, living off of the grid and sustaining herself.

Lacey continues to document Mary's spiral into Kurt's ego-driven experiment as the two grow closer, engaging in risky drug behavior together trying to understand what they are feeling and what they truly mean to each other. During this time, Mary begins to cling to Kurt because Chandra has left the city to pursue a spiritual community and Mary has few other connections to New York aside from Ed. Kurt brings Mary to a swanky Hollywood gala where she covers her face with a veil as a piece of performance art at Kurt's request. Her appearance brings a dizzying amount of attention, catapulting Mary into Kurt's world of paparazzi and red carpet events. However, after Mary must return to her native Tennessee after her mother's death, Kurt is incensed that she leaves him for the weekend, and their relationship sours. When she returns to the city, Kurt is waiting for her and berates her for leaving unexpectedly. He tells her that she has hurt him, somebody that she loves, confusing Mary because she is still not completely sure what her feelings for Kurt have developed into. He voids their contract, dismissing Mary from the research study.

Mary has continued her PAKing treatment throughout the duration of the experiment, but Ed also cites the psychic connections he can sense between Mary and another person as the reason she must stop her treatment immediately. This also feels like the end of a relationship to the reader because of the heightened intimacy between Mary and Ed as their sessions progressed. As Mary leaves Ed's office she grows puzzled when a young girl approaches her and asks for her autograph and a photograph together. She then finds out that Kurt has used some of the footage of them together and audio recordings of her and the other girlfriends to complete his movie, The Walk, and that a trailer has been released to both widespread acclaim and scathing criticism. Mary retreats fully into herself, not leaving her apartment for weeks.

Months pass and Mary lives her life as a virtual hermit, watching the city from her balcony and cleaning obsessively while listening to the radio. On a random day, she hears a new story about Identity Distance Therapy, a product of Kurt Sky's technology company designed to create a virtual reality relationship experience. She knows immediately that the findings of her research study have been used in the development of this new device and she emerges onto her fire escape, thinking to herself. She reminds herself of her decisions, never passing judgement on whether what she did was right or wrong, as the novel ends.