Mistakes Were Made

Cassie Klein, a 21-year-old senior at Keckley College, goes to an off-campus bar to avoid her school's Family Weekend. She buys a drink for an attractive older woman who introduces herself as Erin. They kiss in the restroom and have sex in Erin's rental car. When Erin mentions she is visiting her daughter at Keckley, Cassie decides not to ask who the daughter is. They part, each assuming the encounter is over.

The next morning, Parker Bennett, a freshman and one of Cassie's close friends, begs Cassie to join breakfast with her visiting mother. At the restaurant, Parker introduces them: The woman greeting Cassie is Erin. Both mask their shock, and breakfast goes surprisingly well. When Parker steps away, Erin warns Cassie that Parker already resents her for divorcing Parker's father, Adam. That evening at Parker's a cappella concert, Erin follows Cassie to a bathroom and they make out before Erin stops things from going further.

Over the following weeks, Cassie cannot stop thinking about Erin. She confides in Acacia, her best friend since childhood and Parker's roommate. Acacia is initially amused, then angry, but ultimately supportive, urging Cassie to get over it and not tell Parker. At a party, Cassie steals Erin's number from Parker's phone and sends a drunken text. Parker grows suspicious, but Cassie lets her believe she is secretly involved with Acacia.

Before Thanksgiving, Parker announces she has bought Cassie a plane ticket to spend two weeks of winter break at Erin's house in Nashua, New Hampshire, framing it as a buffer for her strained relationship with her mother. Cassie panics and calls Erin, who shuts down the conversation with cruel dismissiveness. Erin sends an apologetic text days later.

In New Hampshire, the two settle into a tense but warm routine. Erin has coffee ready each morning before Parker wakes. Cassie calms Erin's anxiety about the annual Christmas Eve party by telling her to stop worrying about what she "should" do. At the party, Adam condescendingly offers Cassie an unsolicited letter of recommendation, implying her gender is merely a diversity advantage for graduate school. Erin confronts him privately, and Cassie overhears Erin defending her. That night, Erin visits Cassie's room and, overcome with feeling, kisses her.

The day after Christmas, Erin tries to create distance by cruelly suggesting Cassie has "mommy issues." Cassie storms off. Erin goes to apologize while Cassie is showering and ends up joining her. They have sex for the first time since the parking lot. Afterward, they establish ground rules: no sex while Parker is in the house, no visible hickeys, and the arrangement ends when Cassie's visit ends. Cassie jokes that she promises not to fall in love with Erin. They break every rule. On New Year's Eve, Cassie sneaks upstairs to kiss Erin at midnight. On Cassie's last morning, they share a long kiss at the airport.

Back at school, their connection intensifies through screens. For Valentine's Day, Cassie sends flowers to Erin at work, and Erin calls her "babe" for the first time. A FaceTime call that evening escalates into phone sex. In therapy, Erin confesses the situation to her therapist, Carolyn, who does not judge her.

Parker, however, was on Cassie's computer on Valentine's Day when Erin's text appeared. She confronted Acacia, who confirmed the relationship. Furious, Parker gradually withdraws, skipping Monday breakfasts and becoming unreachable. Cassie attributes the distance to Parker's new relationship with Sam. In late February, they have a blowup: Parker accuses Cassie of having no "models of good relationships," and Cassie fires back that Parker has abandoned her friends for Sam.

Erin finally explains to Parker over the phone why she divorced Adam: She wanted to model what it looks like to pursue happiness rather than live by others' expectations. Parker cries but says she is happy for Erin. Parker then tests Cassie by arranging for Gwen, a graduate student, to flirt with Cassie at a party. Cassie turns Gwen down. After Parker and Sam break up, Cassie stays with Parker for the weekend, and they reconnect and exchange apologies.

During spring break, Cassie secretly interviews at United Aerospace Laboratories (UAL) in Boston, receives the offer, and calls Erin first. Erin drives ninety minutes to celebrate. At the hotel, they spend an entire night together. Erin reflects that they are essentially dating but refuses to name it, telling herself Cassie should go to Caltech and the relationship should become a memory. Cassie, accepted to every graduate program she applied to, quietly begins reconsidering whether she wants to move across the country.

Parker and Cassie's friendship fully restores. Erin helps Cassie find a Boston apartment. Acacia points out repeatedly that Cassie and Erin are dating; Cassie denies it. At graduation, the Webb family, Acacia's parents and brother who serve as Cassie's surrogate family, surprise Cassie. Erin sends a motorcycle as a graduation gift. Over the summer, Cassie rides to Nashua most weekends, and Erin visits Boston. Rachel, Erin's best friend, meets Cassie and later confronts Erin, noting the relationship is serious and that Erin is happier than she has been in years. Erin insists it cannot work but admits she is letting herself have this summer.

One evening, Cassie overhears Erin telling Rachel she cannot just date her daughter's friend. Cassie retreats without hearing the rest. During an encounter at Cassie's apartment days later, Cassie nearly says "I love you" and catches herself.

The Friday before the Fourth of July, Cassie arrives at Erin's for a planned evening alone. They are kissing in the kitchen when Adam walks in unannounced and begins shouting. Parker appears behind him, tells Adam to leave, and reveals she has known about Erin and Cassie since Valentine's Day. Acacia helped Parker see how happy they make each other. Erin breaks down crying.

Cassie, overwhelmed, leaves on her motorcycle. She calls Acacia, who calms her down. She reflects on her lifelong pattern of running, from her mother's home, from friendships, from vulnerability, and decides she does not want to escape anymore. She stops to buy purple swim fins, a reference to Erin's dream of scuba diving and her favorite color. Back at Erin's, Cassie holds up the fins and delivers a stumbling speech: The ocean is huge and terrifying, but she wants to go with Erin because life feels less scary beside her. Erin confesses she was not dismissing the relationship but talking herself out of admitting how much she wanted it. They confess their love. Cassie reveals she has been considering MIT instead of Caltech, for Acacia, for her job, and for Erin.

That weekend, Cassie and Parker have a full, honest conversation. Parker describes her journey from rage to acceptance, and they affirm each other as best friends. At the Fourth of July fireworks, Parker tells Cassie to kiss Erin already. Cassie does, surrounded by fireworks and their entire friend group.

In an epilogue set years later, Erin commissions a ring with aquamarine and meteorite, and Cassie separately buys one after Parker gives her blessing at her own college graduation. On the Fourth of July at the lake house Erin and Cassie share, Erin drops to one knee first, referencing their scuba-diving metaphor. Cassie shouts "No!" because she had planned to propose herself, then says yes. She pulls out her own ring and kneels. They both say yes, kissing as fireworks explode over the lake.