The season 5 premiere picks up where the season finale left off. At Ross and Emily's wedding, Ross has made a serious Freudian slip:
Minister: I, Ross…
Ross: I, Ross…
Minister: …take thee, Emily.
Ross: …take thee, Rachel.
Oops. Rachel wonders aloud whether she should go up to the altar, but Emily instructs the minister to go on with the ceremony. She is clearly livid, and the newlyweds share a very cold first kiss. They walk out of the church together, and once outside, Emily socks Ross in the stomach.
At the reception, Ross and Emily are fighting in the bathroom while the other friends listen at the door. Ross comes out of the bathroom alone, and worries that nobody seems to be having fun at his reception. Emily's stepmother's cell phone rings, and it's Phoebe again. She tells Mrs. Waltham that she is Dr. Phalange, Ross's personal physician, and that Ross forgot to take his brain medicine, meaning that women's names are interchangeable in his brain, through no fault of his own. Unfortunately, Mrs. Waltham doesn't buy the story.
Chandler approaches Monica in the buffet line. The two had made plans to meet up that night, but Chandler is worried what continuing their affair might do to their friendship. Monica wonders how they could have let this happen, and blames being away in a foreign, romantic country. With this logic, Monica and Chandler decide that while they're still in London, it only makes sense to keep having sex. They decide to meet in the wine cellar in a few minutes.
Monica tries to make her escape to the wine cellar, but Rachel stops her, wanting to talk about Ross saying her name and what it could mean. Monica tries to shake her off, but when Rachel decides to talk to Ross about what he thinks it meant, Monica tries to convince her to stay away, since he's married now. Turns out the meet-up in the wine cellar isn't in the cards anyway, as Emily's father is giving guided tours of the room. Monica and Chandler see Joey eating steak, even though he promised Phoebe he wouldn't eat meat until the babies are born. He uses the excuse that they're in another country so it doesn't count. Monica and Chandler, having used that reason to excuse their own behavior, let him off the hook.
Rachel approaches Ross, who is still lingering outside the bathroom waiting for Emily to come out. She pries a little into what happened at the wedding, hoping to get Ross to admit he said her name because he still has feelings for her, but he insists it was just a mistake and that he loves Emily. Joey comes over to tell Ross that the band is waiting for his first dance with Emily, and remarks that Emily sure is taking a long time in the bathroom. Rachel jokes that when she locked herself in the bathroom at her wedding, it was because she was trying to climb out the window and take off. Ross barges into the bathroom, and sure enough, there's an open window and no Emily.
Monica and Chandler head up to Monica's hotel room, but find that Rachel is already there. They almost manage to shake her off by telling her they need to change and will meet her downstairs, but then Phoebe calls the hotel room and she and Rachel talk about what Ross's name reversal meant. Monica and Chandler decide to go "change" in Chandler and Joey's room instead. That plan is thwarted too, however, when Joey comes home with a girl, and insists Monica and Chandler vacate the room.
Next stop: Ross and Emily's honeymoon suite (apparently all the friends have keys to one another's hotel rooms). Monica feels guilty for using her brother's honeymoon suite, but Chandler talks her into it. However, as they pull back the covers, Ross bursts in, looking for Emily. He decides he should stay in the room in case Emily tries to find him. Monica and Chandler try to leave, but he asks them to stay and keep him company, and they can't say no.
Quite awhile later, Ross is asleep with his head in Monica's lap, while Monica and Chandler lament their thwarted plans to have sex again. A knock on the door wakes Ross up. He hopes it's Emily, but it's only her parents come to get her things. Emily's father tells Ross that she's gone into hiding, and never wants to see Ross again. Ross tells him to tell Emily that he will be at the airport waiting to catch the flight for their honeymoon, and he hopes Emily will be there too. Emily's father agrees to give her the message.
Monica and Chandler are sitting next to each other on the plane ride home. They decide that maybe it was for the best that they never got together again, as it made their one night together more special. Chandler comments that they're still over international waters. Monica goes to the bathroom, with the idea that Chandler will join her there in a minute. As soon as she leaves, however, Joey takes her seat and engages Chandler in a conversation about his future as an actor. Monica returns from the bathroom a half an hour later, and Joey is still talking to Chandler.
Back at the apartment, Monica, Chandler, and Joey say hi to Phoebe. Joey and Phoebe go home, leaving Monica and Chandler alone at last. Good thing they have that "not in New York" rule. Monica thanks Chandler, telling him that night in London meant a lot to her, since she was going through a hard time. Chandler says the night meant a lot to him too, because Monica is really hot. The two hug, and Chandler leaves. He comes back in a minute later, saying, "I'm still on London time, does that count?" "Oh, that counts," Monica says, and they kiss.
At the airport, Rachel is on standby for a flight to New York, when she passes Ross, sitting at his gate, waiting for Emily. It is the final boarding call for Ross and Emily's flight to Greece, and Emily has not shown up. Rachel convinces Ross that he should go to Greece without Emily, to clear his head. Since she doesn't have a ticket home, he offers her Emily's ticket to Greece. As Ross and Rachel get on the plane, Ross realizes he's forgotten his jacket in the waiting area, so Rachel goes on ahead. As Ross goes to get his jacket, he sees Emily, who's shown up at last. However, she's just seen Rachel get on their plane, and she's not too happy about it. She runs away, and Ross runs after her, leaving Rachel alone on a flight to Greece.