Warning: Major spoilers ahead

Elizabeth and Greg meet up with Katie for breakfast at the inn, though things are still tense between them after the truth about how she got her job at the school came out.

While Greg thinks the parents are putting on a united front, Elizabeth washes her hands of any blame and pins it squarely on him, saying he asked her to pull the strings for her.

Greg admits that, following the divorce, he was lonely in Florida. He didn’t want Katie to be in a similar situation after her split from Archie, so did what he could to keep her on track. He apologises for overstepping.

Katie says that her life is her own, and as long as he promises to stay out of her business from now on (even if she decides to start doing meth), she’s cool with him.

With things now settled, Elizabeth reveals she doubled booked this heart-to-heart with a meeting with board member Graham. Katie questions how Greg thought he was ever a good match for her. Greg tells her she can get away with it when she’s as hot as she is.

In class, Archie is aloof and quiet, and the class notices. He tries to snap out of it and talks about the ups and downs of modern Russia, before paying some respect to Mikhail Gorbachev – the Soviet leader who some criticised for putting his wife front and centre, even ahead of the union. He even made a CD dedicated to her after she died titled ‘Songs For Raisa.’

It’s clear this is all an analogy for his relationships with Sunny and Katie, and when he starts crying, he dismisses class and makes a hasty exit.

In Greg’s last lecture ahead of the Christmas break, he recommends they all watch It’s a Wonderful Life, and gets emotional as he dismisses class, urging them all to keep writing. He then asks Tommy to make sure he gets his final chapter draft in to him as soon as possible so he can give him a passing grade.

Tommy promises to get it in by the end of the day but wants to make sure it’s the best it can be. He also shares that he’s managed to get back on track in his other classes, passing them all (just about).

At Sunny’s house, Mo is upset that she’s been given a B in one of her business classes. Archie is there, but still distracted – something Sunny notices because he’s being nice to Mo (to a point). When Archie leaves, Mo notes how much she’s going to miss rooming with Sunny, as she prepares to move to Wisconsin with Archie ahead of the baby’s arrival.

Meanwhile Archie heads straight to Katie, declaring he’s made a decision about their marriage, and wants to make it work. The pair kiss, with Katie excited about reuniting with her husband.

In the library, Greg is catching up with Dylan when Tommy arrives to deliver his final paper. Dylan notices how much he admires Greg, and how much of a shame it is that he’s leaving at the end of the semester. She notes that a lot of people will miss him, including her. She tells him she’s glad they didn’t sleep together on their first meeting, as she has a habit of falling out with people afterwards – and she will miss talking to him after he’s left. Greg reminds her that they both own phones.

Greg gives her the first copy of his new book – and the first written from a female perspective. She’s excited but, despite Greg telling her he had no say in the cover, is disappointed when she sees image is of a busty woman whose head disappears off the page. To poke fun at him, she calls over his super-feminist student Ronni, who berates him.

In the cafeteria, Katie shares with her friends that she’s getting back together with Ronni. They’re theatrically unhappy with her but ultimately decide to support her.

Meanwhile Archie tries to make peace with Greg in the teacher’s lounge, excitedly telling him they’ll need to find common ground now that he’s back with Katie. This is news to Greg, who still hates Archie for cheating on his daughter.

Greg vents to Elizabeth. While she shares his feelings towards Archie, she urges him to leave Katie alone considering the promise he’s only just made to her. Instead, he suggests they both get drunk.

Archie calls Sunny into his office to talk, and she knows immediately something is wrong. He tells her that he “really has to see his marriage to Katie through”. Sunny is surprised by how much his decision hurts, saying he’s making a mistake and is choosing the wrong path.

She tells him she’s leaving the next day for Wisconsin and if he wants to join her, he needs to be at the apartment by 8pm. He leaves nothing to doubt, and says he won’t be there. She leaves.

As drinks flow at Greg’s house, he and Elizabeth bond over their now shared attachment to Ludlow College. She asks why he’s actually leaving, and he says he feels like he’s cramping Katie’s style. Elizabeth encourages him to make decisions for himself, not for other people, and if he enjoys being at Ludlow he should stay.

As she leaves, she makes a pass at him, which he turns down, saying that he spent too long getting over her to do that again. She apologises, but tells him to bear that in mind when it comes to Katie, who is now having to get over Archie and is surely having the same problem he had.

The next day at work, Greg pulls Tommy into his office to praise him for doing such a good job with his final chapter. Tommy asks for more feedback, and Greg speaks about the lead character Boone, and how Tommy detailed his internal crisis. He adds that “sometimes people know who they are, but they need one tiny thing to wake them up”.

Tommy tells Greg he’s had plenty of one-on-ones with teachers before but this is the first time he’s actually enjoyed it. He invites him to the diner for a last goodbye, offering to give him free fries, before leaving excited about his future.

We then cut to Katie in the cafeteria, who is having lunch with Archie and watching him talk through their Christmas plans. She tells him he has spinach in his teeth, and as he tries to get it out and fails, something clicks and she tells him she can’t be with him before quickly leaving.

Archie tracks her down in the lecture hall and asks what’s going on. She says that no matter what “he’ll always metaphorically have spinach in his teeth”, but he doesn’t understand what she’s saying.

She says that he’ll never be the person she needs him to be, and now the decision to leave is hers, it’s now clear they need to be apart. She admits that she was disappointed in herself for taking him back and declares herself a “rockstar” – the nickname Greg has always given her but she hated.

Archie tells her that he sabotaged his relationship with the mother of his child for her, but she won’t let him make her feel guilty, saying he was the one who started all that. She tells him she hopes he ends up happy but wants a divorce.

Greg leaves Dylan a Christmas present – his e-bike – outside her house as she’s not in, before heading to the diner. When he gets there, he’s surprised by a party in his honour, as Tommy declares “It’s a Wonderful Life” (still having not seen the film). Dylan is also present, saying this is how much everyone at Ludlow care about him.

Greg is taken aback and touched by the gesture, before grabbing a beer from Walt and joining in with the celebrations.

Archie runs to Sunny’s house to make up with her. He’s there by 8pm, but Mo tells him with relish that she and Sunny’s dad Fred arranged an earlier flight for her. She tells him to lock up after he goes and then leaves for the Christmas break.

The party goes into full swing at the diner, with Greg chatting to Walt ending an unheard conversation with a handshake and “to be continued”. Ronni begrudgingly admits that she read Greg’s new book and didn’t hate it. Everyone is in high spirits, grabbing photos, sharing hugs, and Cristle – now dating ice hockey coach Jake - grabbing one last passionate kiss from him as a goodbye.

Tommy thanks him for changing his life, but Greg says he did that himself. Dylan then forces him to give a speech to the crowd, and he thanks everyone for being there, and gets emotional as Katie comes through the door. He admits that his time at Ludlow made him feel like he belonged somewhere for the first time, and he’ll never forget it.

As the party winds down, Katie and Greg walk home together in the snow, and she shares that she's ended things with Archie for good this time. He tries to play it cool but eventually gives in and cheers with relief.

He admits he’s going to miss being at Ludlow, and she tells him not to leave on her account. When he says he doesn’t want to complicate her life, she lets him know he would do that anywhere, so it might as well be at Ludlow.

That night, he calls Walt and asks him if it would be possible to stay on for another semester. Walt says it would make a lot of people happy, and that way they could have their “last hurrah” together.

When Greg asks what he means by that, Walt informs him that the school board has elected Elizabeth as the new school president – effective after the next semester. Greg is shocked, and asks if he’s OK, but Walt simply tells him that he’s going to enjoy the beautiful night and wishes him a merry Christmas before dunking his head underwater in his ice bath.