Sonia Friedman, portrayed by Cristin Milioti, is a thirty-something woman who experiences a moment of panic when her live-in boyfriend, Chris Jensen Dan Soder, proposes to her. Unsure of the commitment, she declines his proposal, causing him to walk away hurt. Shortly after, her close friends—Nora, Halley Feiffer, Lee, Kate Simses, and Anna, Erica Sweany—come over to offer their support. Through a series of flashbacks narrated by Sonia, we learn that Lee and Anna are a married couple, while Nora is engaged to Mark [Mark Gessner], who is also their mutual friend.
A glimpse into Sonia’s past reveals that she met Chris through Mark six months before the proposal, and nostalgic moments showcase Chris teaching Sonia to dance to the romantic tune "It Had to Be You." The following morning, Chris finally confronts Sonia, reminding her that they have been together for over a year. He reflects on how their friends' marriages should have encouraged Sonia to reconsider her stance on marriage. Although she apologizes, they agree that she needs some time to reflect on her feelings.
With Sonia left in solitude, she begins an inner dialogue illuminated by flashbacks and animated sequences. This exploration prompts her to identify three key fears about entering marriage with Chris: the trepidation of their incompatibility, worries about their sexual chemistry, and her belief that she has not yet matured into "a woman." These fears manifest in a fantasy about a fellow commuter, whom she sees as having an enviable, perfect life.
As Sonia returns to reality, she logs into her personal website—a thoughtful gift from Chris that she once rejected. Despite her complexities, she decides to go out with Chris to watch a movie for which she had even created the soundtrack, leading to their first intimate night together at her place.
In the present timeline, Chris, Sonia, Nora, and Mark are together as friends, and they discuss Mark and Nora's recent purchase of a new home, motivated by Nora’s pregnancy. However, Mark ultimately encourages Chris to press Sonia for a decision about their future together. Feeling the weight of this ultimatum, Chris confronts Sonia again, expressing his love and desire for a committed relationship, yet he cannot continue their current dynamic indefinitely. This leads to a tough conversation about putting their relationship on hold until Sonia is ready.
While shopping, Sonia coincidentally meets Lara [Rachel York], a woman she often commutes with, leading to an unexpected exchange of shopping bags. When Sonia finds Lara’s blue thong in the mix and tries it on, it gives her a bold, new perspective. Prompted by Anna's suggestion for a getaway, Sonia decides to escape to Rome to reconnect with her college crush, Fabrizio [Danny Deferrari]. In Rome, she engages in a wild, reckless night with Fabrizio and his brother, Dezi [Nico Grelli], but upon waking, she discovers a note revealing Fabrizio is married and has stolen her cash and phone.
Back in New York, Nora shares that Chris has moved in with her and Mark after their breakup. She invites Sonia for dinner to reunite with Chris casually, although in a twist of fate, Chris isn’t present when Sonia arrives. When she finds herself arriving late due to work commitments, she walks into a tense scene with Nora and Mark at odds over their birthing choices, and Chris opts to go elsewhere to avoid an awkward reunion.
Three weeks post-proposal fallout, at Mark and Nora’s wedding, Sonia is eager to sit next to Mark. Although he reluctantly agrees, he remarks that he doesn't wish to converse, yet they end up dancing and reconnecting. During a vulnerable moment, Chris admits he still has feelings for Sonia. The next morning, they find themselves back together, but Chris receives a tempting job offer from Google in San Francisco. Sonia, sensing his desire for independence and fearing they’d revert to their non-committal ways, encourages him to pursue the opportunity, prompting Chris to choose the job and end their relationship.
In another turn of events, Lee discloses her own pregnancy to Sonia, catalyzing Sonia’s realization that it’s time to take action. She resolves to propose to Chris and prepares a sentimental DVD showcasing their memories set to "It Has to Be You." However, Mark informs her that Chris is in Pennsylvania visiting family. In a moment of spontaneity, Sonia boards a bus to catch up with him, accidentally running into Lara once more. This encounter leads Sonia to understand that Lara's seemingly perfect life is not what it appears to be.
Meanwhile, tension builds as Nora goes into labor, and Sonia is disconcerted to learn that Mark has left the family visit to be there for the birth. In a burst of determination, Sonia persuades the bus driver to let her off early, making a dash to the hospital to witness the birth. As Chris prepares to leave the room, Sonia begs him to watch her proposal video. Unfortunately, the DVD fails to play the sound, causing her to sing "It Has to Be You" on the spot. The room gradually joins in, creating a heartwarming moment filled with emotion. Finally, when the words "WILL YOU MARRY ME?" flash on the screen, Sonia drops to her knees and asks the pivotal question. Chris responds joyfully, "Of course I will," leading to a beautiful kiss and the beginning of their new chapter together.
