A.C.O.D.

During Carter Spencer's ninth birthday party at the family lake house, his parents begin shaping his perception of love, loyalty, and control through emotional manipulation. The event establishes the pattern of strained interactions that colors his childhood and adolescence. The setting at the lake house frames future conflicts.

Trey spontaneously proposes to his girlfriend Keiko and asks Carter to get their feuding parents to cooperate for the wedding. Carter agrees to try, despite years of silence and resentment between Hugh and Melissa. The request sets the central mission of the film.

Seeking guidance, Carter consults Dr. Lorraine Smith and discovers he was one of her subjects in a best-selling book about children of divorce. He reads the entire book, astonished by how his childhood story has been turned into someone else's narrative. The revelation fuels his plan to regain control.

Carter secretly arranges a meeting where Hugh and Melissa are forced to confront each other at the same restaurant. He tricks them into a lunch where the meal is ordered and paid for, trapping them until they agree to be civil for the upcoming wedding. The tactic marks a turning point in his campaign.

After the lunch, Carter and his siblings regroup and feel closer to an informal truce between the parents. He warns Trey not to count on money, to rely on genuine cooperation instead. The tentative détente gives them hope for a peaceful wedding.

Hugh's new wife Sondra drops a painting at the restaurant as part of her subletting arrangement. Dr. Smith appears on the scene and unexpectedly encourages Carter to participate in a new book about adult responses to divorce two decades later. Carter initially resists but is eventually persuaded.

Carter checks with Trey and discovers his parents are secretly having an affair, witnessed in the Spencer family kitchen. He rushes to share the shock with his long-time girlfriend Lauren, and later learns that Gary has quietly provided a large check to the stepsons. The revelation deepens the personal stakes of the plan.

Dr. Smith analyzes Carter's behavior as a reaction to childhood trauma and the need to remain in control. Outside, Carter unexpectedly meets Michelle, another of the subjects tied to the past. The parallels between their stories heighten the sense that the past is inexorably shaping the present.

At the tux fittings, Hugh fails to show up again. Carter then tracks his mother to a Pilates session, discovering the ongoing deception. Later, Keiko's parents meet the Spencers at a tea house where both Hugh and Melissa finally acknowledge the affair.

Carter brings two boxes of divorce evidence to Dr. Smith, hoping she will confront his parents. That evening, Melissa visits Carter's restaurant, and they share a kiss, complicating his relationships as wedding plans loom. The personal fallout intensifies the saga.

During the cake tasting, Carter finally reveals the parents' affair to Trey, who is supposed to help keep it contained. The fallout leads Sondra to file for divorce from Hugh and to evict the restaurant from their orbit. The wedding plan teeters on the edge of collapse.

Confronted in the family garage by his parents and Trey, Carter quits the family and kicks them out, pausing Keiko's wedding. The moment marks a decisive break with the spiraling dynamic. The household fractures as the truth comes to light.

At Lauren's parents' 30+th anniversary party, Carter proposes, but Lauren is mortified and breaks up with him. The rejection underscores how his pursuit of control has strained their relationship beyond repair. The personal cost of his crusade becomes clear.

Carter retrieves the divorce evidence box to the lake house intending to burn it, but Gary arrives and Sondra's carelessness leads to the lake house burning down. The symbolic destruction marks the end of the old era and the beginning of a new phase for the family.

Time passes as A.C.O.D. has its first reading including the adult subjects. Lauren returns to talk with Carter, hinting at reconciliation. One year later, the three Spencer men stand outside a church in identical suits, gathered for a wedding that signals a fragile, tentative unity for the future.