Adam gets a call from his ex-girlfriend Allison, who is inviting him to her wedding. He is reluctant but she is persuasive, explaining that when he gets married, she will come to his wedding. Adam finally agrees.At work, Adam is sitting at a conference table and his work is being praised. Adam edits documentaries, and his current project is a nature documentary. Later, his co-worker Claire says he needs to get out and be with friends. She and Mark go bowling with him but he is too depressed under the circumstances to enjoy it. He throws a ball once and it goes in the gutter.Adam goes to a restaurant with his current girlfriend Helen, but it doesn't go well. First he proposes to her and she is very happy, then he says he wants to break up with her and she leaves angry.While listening to Tony Bennett's "I Left My Heart in San Francisco" on vinyl, Adam remembers his life with Allison in flashbacks.Adam decides to go to San Francisco to attend the wedding. There are more flashbacks.Adam checks into a hotel where the overly enthusiastic Rohan wants to make sure if there are going to be any guests that Adam is prepared for them. No, Adam explains, he is by himself and no one will be joining him.In a bookstore, Greg sees Adam and is very happy to see an old friend. Adam pretends to know Greg but doesn't seem to. Greg says Adam and Allison were the perfect couple and were together so long that surely they would still be together.In flashbacks, Adam recalls how he met Allison, first seeing her at the college library (with purple hair) from a distance and then talking to her as she read a classic novel, and spoiling the ending for her. Somehow, they hit it off and Allison is willing to have a relationship with Adam.Adam attends a dinner with the couple and he meets Aaron, who is happy to see him. Adam has to explain who he is to others who do not know him, and one man gives away his big secret, the one he doesn't want to tell--he was "Literally, right before Aaron". Adam meets Allison away from the others and enjoy getting together again but their pleasant conversation is interrupted when Allison is reminded this is her dinner. Aaron invites Adam to play tennis.Adam goes out jogging and visits his mom Deb, who is happy to see him. He does not explain his presence and when Deb invites him to stay with her, he says a hotel room has been arranged for him. Seeing his mother kept a photo of him and Allison together, Adam tears it up to his mother's dismay.Adam and Aaron play tennis. Aaron says he could have gone pro but he hurt his knee. Adam isn't very good but he tries to be pleasant.Adam goes out jogging again, this time to a clothing store where he knows Allison works. When she closes the store and sees him, Adam tries to claim it was a coincidence that he picked this street. Allison and Adam walk out to a pedestrian bridge over the bay and have a nice time together. Allison says she was promoted to manager. They ride a cable car together and then go their separate ways.Mark and Adam communicate through computers, and Mark tells Adam he shouldn't attend the wedding alone. He has a cousin Talula. Adam reluctantly agrees and he and Talula meet, Adam explains his situation, and Talula agrees to go with him.At the wedding, Adam sits with Talula and the moment arrives when the pastor asks if anyone can show just cause why these two should not be wed. Adam stands up and walks up to Allison and kisses her, to cheers from the audience. Then Adam and Allison walk down the aisle together with the audience still cheering. Then the pastor asks if anyone can show just cause why these two should not be wed, and Adam stands and starts to talk but all he can do is cough, and the wedding finishes normally.At the reception, Adam tries to cope with the situation. He meets Allison's mother Wendy and they have a nice talk. Aaron makes a big announcement that he studied with chef Jean-Pierre in Paris, and then reveals a huge cake. Adam goes out to smoke, and Federico, who is dressed as if he is in charge of the food, is also smoking. Adam explains his situation and Federico gives advice, mentioning Tom Petty song titles. Federico likes Petty so much he named his goldfish Tom Petty.Adam goes back inside and has a talk with a little boy named Emerson who tells Adam he is too young to use that kind of language. Then Adam dances like everyone else. Then he hides out in the restroom (it's never explained why he is in the ladies') and Allison comes in with Leandra, one of the bridesmaids. Allison is surprised to discover Adam in there but they have a serious talk about why they broke up. Allison doesn't want to do that on her big day, but she explains how things didn't work, and Leandra tells Allison she is needed.When they return to the reception, Allison's father gives a toast, and Adam walks up to the cake and pushes it over. Aaron chases him out into the street and Allison follows. Adam is hit by a car but walks away, Allison looks concerned. Then Adam disappears as a bus passes. He gets on the bus.As the credits roll, Adam is shown in the mountains during cold weather, then in a boat in a lake surrounded by mountains when it is not as cold, then hitchhiking with mountains in the background.