NOTE: This spoiler was submitted by Jeremy

The film opens in the early 1970’s at the prestigious Barton Academy. Paul Hunham (Paul Giamatti) is a tough and bitter professor with a sight problem. His boss Dr. Hardy Woodrup (Andrew Garman) is displeased after Paul previously failed the son of an influential senator, who had personally aired his grievances with the school for this decision. Paul stands by his decision and states that the senator’s son was an idiot.

Among the students at Barton is Angus Tully (Dominic Sessa), a noted troublemaker who is looking forward to joining his mother for the holidays in Saint Kitts. He is antagonized by another student, Teddy Kountze (Brady Hepner), over something that Kountze claims Angus took from him and isn’t giving back. The boys later gather with their teachers in the school’s chapel over a Sunday service, where the school is honoring Curtis Lamb, the deceased son of the school’s lunch lady Mary (Da’Vine Joy Randolph).

During one of Paul’s classes, he gives all the boys poor grades except for Angus, who gets a B+. After the students complain, Paul offers a makeup test, but focusing on new material. Angus tries to speak up for the class, but it only makes Paul decide to leave the previous grades as they are.

The holiday break arrives, and the majority of students go home. Angus talks to his mother Judy (Gillian Vigman), who tells him that she and her husband Stanley (Tate Donovan) are going to take a belated honeymoon, despite Angus’s protests since this means he will be forced to stay at the school. He, along with Kountze, Jason Smith (Michael Provost), Alex Ollerman (Ian Dolley), and Ye-Joon Park (Jim Kaplan), are left behind as well in the care of Paul and Mary.

Angus and Kountze get into a fight after the latter takes a picture belonging to Angus. Alex snitches on Kountze and gets him in trouble. During dinner, Kountze is separated from the other boys while they eat. He makes a rude remark about the food and Mary’s cooking while bringing up her loss, causing Paul to snap at Kountze for his behavior. Paul later talks to Mary privately about Curtis, who had enlisted in the Vietnam War as a means to help him through college.

Paul makes the boys continue studying and go through a strict routine, such as early morning workouts. While outside, Kountze bullies Alex for telling on him and throws one of his gloves away so he loses it. At night, Angus hears Ye-Joon crying since he is far away from his family. He has also wet the bed from a nightmare.

Paul contacts the boys’ parents, and all but Angus’s parents are able to bring them back home. Paul and Angus get into a shouting match, which ends when Angus makes a jump in the gym and ends up dislocating his shoulder. Paul rushes the boy to the hospital where the doctor and nurse pop his shoulder back into place.

Afterwards, Paul takes Angus to a diner where they find another teacher, Lydia Crane (Carrie Preston), who is picking up extra shifts during the holidays. Angus steps away to play on a pinball machine and ends up getting on the bad side of two other patrons. When they attempt to escalate things into a fight, Paul smooths things over by offering to buy the men beer. They agree and back off, though Angus thinks Paul let them off too easily.

Angus later brings up how Lydia invited Paul to a Christmas party and wants to go since he’s been cooped up in the school too long. Mary agrees and joins the two, along with another companion named Danny (Naheem Garcia). Angus hits it off with Lydia’s niece Elise (Darby Lee-Stack) as he helps her with activities with kids, and they share a kiss. Paul is disappointed when he finds Lydia’s boyfriend showing up, as he had previously hoped to court her. Mary then gets too drunk and emotional over Curtis, leading Paul and Angus to walk her out. When Paul says that going to the party was a bad idea, he and Angus argue until Paul says he was hoping Angus’s father would come take him away, which leads to Angus saying his father is dead before storming off. Mary then berates Paul for his words.

On Christmas Day, Angus states that he wants to go into Boston rather than be stuck at the school. Paul relents, and Mary goes along so that they may drop her off at her pregnant sister’s home. Paul and Angus end up spending the day together, bonding and making jokes together over subjects such as Paul’s sex life.

The next day, Paul catches Angus sneaking out in a taxi. When pressed for it, Angus admits that he was going to visit his father. Paul decides to go along with it, thinking they are going to a cemetery. In truth, Angus’s father Thomas (Stephen Thorne) is alive and is institutionalized. Angus visits him and tells him about what he has been up to, hoping that Thomas can be sent home. Thomas simply responds that he thinks the staff are doing something to his medicine. Angus leaves, disappointed. He later goes out to dinner with Paul and expresses his fears that he will end up like his father, and he thinks this is why his mother tries to spend time away from Angus. Paul states that while Angus is a pain in the ass, he is a brilliant young man and will not be anything like either of his parents.

Paul, Angus, and Mary later return to Barton. After the holidays are over, Angus reunites with his classmates and laughs over Kountze getting sunburn on his face. Paul is then called to Hardy’s office to meet Judy and Stanley, as they learned about the “field trip” and how Angus visited Thomas, who now believes he is ready to come home when he is not in any condition. Judy believes Angus talked Paul into taking the trip, which would get him kicked out of Barton. Paul covers for Angus and says the trip was his idea and that he encouraged Angus to talk to his father. This gets Paul fired, but Angus is allowed to stay.

Paul packs up his things and says goodbye to Mary. Before he drives off, Angus meets with him one last time and receives some final advice from Paul before they simply shake hands to avoid a sappy farewell. Paul then drives away from Barton forever.

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Paul Hunham is a tough and bitter professor at the prestigious Barton Academy. One of his students, Angus Tully, is intelligent but constantly getting into trouble so much that he has been kicked out of multiple schools. Angus ends up among the few students forced to stay behind at Barton for the holidays since their parents cannot bring them home, leaving them under the care of Paul and the school's lunch lady Mary Lamb, who lost her son Curtis in Vietnam.

Angus is left as the last student behind after the other boys' parents pick them up. He ends up bonding with Paul despite their differences, culminating in them and Mary taking a trip to Boston on Christmas. Paul and Angus end up visiting Angus's father Thomas, whom Angus had previously stated was dead, but is actually institutionalized. Angus worries he will end up like his father, but Paul tells him he is a brilliant young man and that he will be nothing like his father.

Angus's mother and stepfather learn about the trip, which has proven problematic for them with Thomas wanting to come home. Paul lies and says that the trip was his idea so that Angus will not get kicked out. Paul is fired but appears to have gained a mutual newfound respect for Angus just before he leaves Barton.