After a flashback of little Kevin making a valentine for Sophie, Kevin wonders what time it is. It's right before the wedding rehearsal dinner. KEvin is enamoured with the wedding singer. Also he runs into Cassidy, and then finds an obnoxious cousin of Philip's who is also single.
Sophie arrives and Rebecca thinks that she and Kevin are still in college and married.
Meanwhile, the wedding singer asks Kevin to help her out so she could escape Oliver. He hugs her and they talk til his kids show up and want to know if they can have smores. Madison walks them off and Kevin spies Sophie arguing with a hotel worker who is insisting a bag is hers when it's not. Sophie tells Kevin the airport has lost her luggage. Stores are closing in half an hour. Also her husband had to work and is not here. Kevin offers to drive Sophie to go get clothes. Kevin has rented a tiny yellow car for Kate and Philip. He takes the Just Married sign off.
They are out of options and go to a cleaners that is about to close. He lets them look through unclaimed clothes. She tells Kevin that after the divorce money was tight so she learned how to go thrifting. While they are looking she asks how the kids are doing. Sophie goes to change and asks Kevin about his GQ profile. He says that was for a nonprofit. Sophie has changed into a green dress.
Next they hit a Whole Foods type store and Sophie says that she is saving lives in Berlin. She is a traveling nurse. After her mom died she found a list she wrote of places she wanted to visit and made her own list. She went to Italy for her honeymoon and then Paris, and began traveling. It is hard with her husband but she can work and then take a stretch off.
Kevin tells Sophie that when Nicky fell off the jungle gym last year he wanted to call her for advice. Sophie is not ready to go back yet. They stop in a field somewhere and check out the view. Kevin is glad she's happy and found someone. She says she is happy but also divorced.
At the engagement party, Kevin meets Grant after accidentally spilling Sophie's drink on her. Now, he tells Sophie he liked the guy. Sophie says Grant is a great guy but they've been over for a while and were going through the motions. She finally has grown up. She's impressed that Kevin isn't bugging her about why she didn't tell him sooner. She also tells him that Rebecca thinks they're still married. Kevin tells her how hard Rebecca's disease is for everyone. Sophie is sorry. She asks if he's dating anyone. He can't find the right person. Sophie is cold. As they walk, Kevin recalls them walking together as kids and teenagers.
At the bonfire, the twins want their smores double stuffed. Kevin sees Sophie sitting across the way. After everyone leaves, he follows her into the elevator.
Kevin walks Sophie to his room. They look like they're about to kiss and then Sophie pulls away ad opens the door instead. They begin kissing and making out. Sophie gets on the bed on top of Kevin. He says her hair smells the same. She says it's not. He says okay. Sophie suddenly says she should go. She says she can't do this. He should like how her hair smells now, not in the past. She says Grant used to pretend to fast forward whenever Kein was on TV and one night she couldn't do that anymore. She realized she couldn't fast forward through Kevin. But it's too much. They have too much history. She doesn't want to go backwards. Kevin says neither does he. Sophie says she can't and runs away.
The wedding singer is now sitting with Kevin at the bar. She orders him a ginger ale and knows it's his drink because she watches people in bars so that she can write songs about them. She has lyrics about someone waiting for someone and wanting to take a chance with them. She gives it to him. Kevin says she is observant. She's embarrassed. He's flattered but says he should call it a night. She tells him to keep the lyrics.
Nicky sees Kevin in the hallways and asks what happened. Kevin doesn't know, but he's done with love. Nicky agrees love is like a game. Dipsy-doodle. A pinball game where he always thought he was done and then found another ball. Cassidy interrupts. She can't get her zipper undone. Could Kevin get it for her? She comes into his room and he unzips her dress for her. She asks to change in his bathroom. In the bathroom she calls out that she should find someone so she doesn't have to keep bothering him and rambles. Kevin reads the napkin lyric and tells Cassidy she's never a bother. He says Nicky thinks she and Kevin should be something. Cassidy says they are not meant to be together and he knows that. They are best friends. She asks if everything is okay. He says he's good. They hug and she leaves.
Kevin lies in bed alone. He gets up and practices his impression for the toast. We see scenes from the wedding. Kevin tells Randall he doesn't know if last night was a good story. Beth overhears and goes to find Madison. Sophie is sitting by herself looking sad and calls Rebecca over to tell her her song was beautiful. Rebecca asks if Sophie is okay. She says it's Kevin, isn't it? She says she loves her son but he is an idiot. She thinks Kevin is still 20 years old and says the timing is off and Kevin isn't ready for Sophie yet. But when the timing is right it will be great.
Randall says that's a lot. Kevin doesn't want to mess things up again with Sophie. Randall tells him all about the Buffalo Bills kept losing the Super Bowl and sold their merch in other countries. The world was insane and made no sense but he and Sophie together makes more sense so Kevin won't screw it up this time.
Kevin goes up to Sophie to talk. Sophie says she prayed for years that Kevin would grow up and he was finally the man she thought he could be. She freaked out because she didn't want them to fall back into the old versions of themselves. She needed him to love her for the woman she is now.
In a flashback Kevin recalls meeting Sophie for the first time and writing a Valentine for her.
Kevin says he has always carried her with him. They kiss. Everyone applauds.