Plot
Since Carter's ninth birthday party at the Spencer family's lake house, his (and his brother Trey's) parents have subjected Carter to emotional manipulation, character assassination, uncomfortable new relationships and witness failed relationships repeatedly via their father Hugh. Not only is he a philanderer, but also a cold, distant father. Their mother Melissa cuts Hugh down relentlessly.
Trey spontaneously proposes to Keiko, his girlfriend of four months, then requests Carter get their feuding parents, who have not spoken for 20 years, to cooperate. Seeking advice from Dr. Lorraine Smith, who he had seen as a teen believing she was his therapist, Carter discovers he had been one of her subjects for a best-selling book on children of divorce. Shocked, he tracks it down, reading it from cover to cover, then formulates an attack plan.
As Carter is inicially unsuccessful at convincing either Hugh or Melissa separately, he tricks them both into meeting for lunch at the same restaurant. With them cornered, Carter coerces them, explaining the meal is ordered and paid for, so they must stay until they agree how to be civil at the wedding.
Meeting up later, the Spencer boys feel content that Carter convinced their parents to call a truce. He tells Trey to not count on money from them, but to continue the planning.
Right after Hugo's domineering third wife Sondra presents the restaurant with an obligatory painting, as she sublets them the space, Dr. Smith appears. Carter has inadvertantly inspired her to write a follow up book for C.O.D., the adult, 20 years later one. Initially, Carter refuses but is finally persuaded.
Sondra calls Carter, asking for details about his alleged golf outing with his father, as she is at her Cornell sorority reunion. Suspicious, he checks with Trey, who believes he is home with a bad stomach. Carter lets himself in, only to find his parents boning in the kitchen.
Carter rushes to tell his long-term girlfriend Lauren, but tells noone else. Unbeknownst to Melissa, her husband Gary presents his stepsons with a large check for the wedding.
Hugh tries to convince Carter it was a one time encounter. Later, speaking with Dr. Smith, she believes Carter now still lives in reaction to the childhood trauma, by making sure he is always in control. Outside, he inadvertantly meets Michelle, another of the subjects.
At the tux fitting, as Hugh gives is again a no show, Carter hunts down their mom, who again has used pilates as an excuse. Later on, as Keiko's parents have not met the Spencers, they meet up at a tea house. Both Hugh and Melissa show up, supposedly separately, but they soon annoy Carter so he storms outside. Now, they admit it is an actual affair.
Carter brings two file boxes from Melissa's with evidence of Hugh's cheating, first obsessively pawing through them, then dropping them at Dr. Smith's, insisting she confront his parents. That evening, Melissa shows up at Carter's restaurant, stays late talking, then they have a make out session.
At the cake testing, Carter finally reveals to Trey their parents' secret affair, then suggests he try to handle it. Botching it, not only does Sondra file to divorce Hugh, but she evicts the restaurant. Confronted in his garage by his parents and Trey who blame him, as Keiko has paused the wedding, Carter quits the family, kicking them all out.
At Lauren's parents' annual 30+th anniversary party, Carter proposes. Mortified, Lauren breaks up with him. Carter takes the box of divorce evidence Dr. Smith returns to him to the lake house, which he has not visited in 20 years, and douses it in gasoline. Before he can light it, Gary appears. Soon, everyone else does too. Soon after Carter discovers that absolutely everyone else has frequented the house, the careless Sondra inadvertantly burns it down with a match.
Carter volunteers to buy what once was the lake house. Time passes, and A.C.O.D. has its first reading, which includes the subjects. Lauren appears, and she goes off with Carter to talk. One year passes, and the three Spencer men are talking outside of a church, dressed in identical suits. They are all summoned into the church for a wedding.
