As Annie Braddock (21), a recent graduate from Montclair State University, embarks on the challenging journey of adulthood, she finds herself at a pivotal moment, grappling with questions about her future and true identity. One fateful afternoon, while enjoying a stroll in the park, Annie's instincts kick in when she heroically intercepts a Segway, narrowly preventing an accident involving a young boy. This chance encounter introduces her to the boy's mother, Mrs. X, who mistakenly addresses her as "Nanny." This misunderstanding marks the beginning of an unexpected opportunity as Mrs. X hires her to look after her son, Grayer. To maintain the charade, Annie fabricates a story for her mother, Judy, claiming she landed a job at a bank, and she discreetly moves into the luxurious X family apartment as their new nanny.
As Annie delves deeper into the opulent lifestyle of the Xs, she quickly realizes that their glamorous facade masks a much harsher reality. Complications arise when she develops feelings for the charming "Harvard Hottie," who lives in her building. Through her experiences as a nanny and her interactions with the "Harvard Hottie" and her close friend Lynette, Annie discovers that he carries his own burdens; he lost his mother at a young age and has faced multiple nannies before ending up at boarding school.
Throughout her deception, Annie continues to mislead her mother with false updates about her job. As her secret life becomes increasingly tangled, an unexpected visit from Judy forces Annie to concoct a ruse, introducing Lynette and her boyfriend Calvin as a pretend couple and claiming their apartment as her own. The truth comes crashing down when Grayer falls seriously ill, leading Annie to reach out to her mother in desperation. During this tumultuous period, Annie overcomes her initial hesitations and forms a deep bond with Grayer, affectionately nicknaming him "Grover." She begins to uncover the tender and loving nature hidden under his unruly behavior, rooted in the neglect he's suffered at the hands of his indifferent parents.
Annie’s newfound awareness extends to Mrs. X, who herself is a victim of her husband's emotional cruelty and infidelity. In her attempts to revive her fading marriage, Mrs. X engages in deception, feigning a pregnancy and weaving intricate lies, but ultimately finds solace in Annie's understanding presence.
When the X family embarks on a trip to Nantucket, Annie is blindsided as she overhears Mrs. X discussing plans to terminate her employment after reviewing footage from a "nanny cam" that captures her affectionate moments with Grayer. The next day, Mr. X's predatory advances culminate in a harrowing assault, leading him to abruptly end Annie's employment, offering a mere $40 as a severance package.
Feeling both enraged and betrayed, Annie uncovers the recording device and uses it to create a damning exposé of the Xs' tumultuous relationship. Mrs. X plans to show this damaging footage at a meeting of Upper East Side mothers, expecting it to prove Annie’s alleged negligence in caring for Grayer. Instead, it reveals the toxicity of the Xs' marriage, forcing Mrs. X to confront the unsettling truths about her own happiness and the facade she has built around her life.
Annie eventually finds comfort with her mother and rekindles her relationship with Hayden (the "Harvard Hottie"). She seeks refuge with Lynette and Calvin while exploring her passion for anthropology, a spark ignited by her experiences with the X family.
As time flows on, Hayden gifts Annie a deeply heartfelt letter from the enigmatic Alexandra. This moving correspondence serves as a tribute to the profound impact Annie has had on Grayer’s life, detailing the remarkable changes in the young boy under her attentive care. The letter reveals that Alexandra has separated from Mr. X and is now dedicated to nurturing a meaningful relationship with her son, which has flourished thanks to Annie's influence.
The words in the letter strike Annie deeply, highlighting Alexandra's gratefulness for coming to appreciate her role in Grayer's life. Notably, it marks a turning point in their relationship, with Alexandra addressing Annie by her actual name for the first time, discarding the previously condescending "Nanny." The letter concludes with Alexandra's name penned in bold strokes, symbolizing the genuine connection and intimacy that has blossomed between them.
