The episode opens with Finn telling Rachel what happened between him and Emma. He's freaking out that he may ruin their wedding. Rachel doesn't think what happened will impact their big day and advises against telling Will.
Finn pays Emma a visit. He wants to talk about what happened but she tells him she doesn't have the time. She reminds him that he will be the best man and therefore standing behind Will at the altar. Will walks in and gives her a kiss.
Will returns to Glee club, telling them he's back "to stay." He thanks Finn and tells him this week's assignment is "Wedding!!!" He's in charge of entertainment at the reception and asks Finn to sing instead of making a best man speech. Will asks the kids to look at romantic love songs.
Emma wants to set Artie up with her niece Betty.
Marley gives Jake an early Valentine's Day gift. She leaves and Ryder walks up. Jake has to admit he hasn't yet bought her anything. Ryder suggests he make it a full week of valentine gifts.
Jake makes a surprise appearance in Marley's history class. Ryder, Sam and Artie help him sing a mashup of two versions of "You're All I Need to Get By" to Marley, who ends up joining in herself.
It's time for the wedding. Before the ceremony begins, Santana and Quinn complain about weddings and men. Artie approaches Betty who is also in a wheelchair. She doesn't seem into the set-up, to say the least. On the advice of Ryder (again) Jake gives Marley flowers. She loves them.
Kurt and Blaine are making out in the car outside the wedding. They talk about what it does or doesn't mean until Mercedes interrupts them and demands that they escort her in.
Sue is wearing an exact replica of Emma's wedding dress to the ceremony. Moments before the ceremony, Emma is panicking. As Will happily sings to the patrons in the church Emma blurts out to herself that she doesn't think she can do it ("Getting Married Today"). Emma runs outside, gets in a taxi and bursts into tears.
The music comes on and Sue walks down the aisle. She gets to Will and tells him "Emma's left the building."
Will and Finn talk in an empty church and discuss why Emma might have left. Will blames himself for leaving her alone. Santana shows up and says Emma's parents still want to have the reception since they paid for it. Will likes the idea and leaves to find Emma.
Using their fake IDs, Santana and Quinn have drinks at the reception and seem to be getting along well.
Jake tells Ryder he thinks he'll be having sex with Marley that night. Ryder doesn't think she's ready. Ryder clearly is having trouble seeing Marley with somebody else.
While Blaine and Kurt sing "Just Can't Get Enough", Rachel assures her that Emma didn't walk out because of him. There had to be more.
Betty is still being nasty to Artie, who for some reason finds her compelling. He asks her to dance.
Tina tells Kurt she doesn't like the way he's treating Blaine. He responds by saying her feelings for Blaine are creepy.
Sue takes the reception stage and makes reference to St. Valentine. She tosses the bouquet Emma left behind and it is caught by Rachel.
Rachel tells Finn she and Brody are calling themselves single even though they live with each other. He thinks she can't commit to Brody because she still loves someone else. He thinks they're eventually going to get back together.
Finn and Rachel sing "We've Got Tonite." Quinn and Santana slow-dance to the song. We see Finn and Rachel going into to a hotel room together. Kurt and Blaine do the same, as do Jake and Marley, Artie and Betty, and ... Quinn and Santana. Rachel and Finn get undressed and hop into bed together.
After hooking up, Blaine asks Kurt if this means they're back together. Kurt isn't willing to go that far. Quinn and Santana also sleep together, with Quinn seeming to enjoy herself. Artie and Betty also had fun together.
Marley doesn't go through with it and Jake seems fine with that decision.
Rachel sneaks out of their room with Finn still asleep.
Rachel returns to New York to find Brody has spent days decorating their apartment for Valentine's Day. He asks her if she kissed anybody while she was gone. She doesn't say much of anything. He tells her he stayed at home while she was gone, but we see a clip of him leaving a hotel room with a bunch of cash. She passes on sex, saying it is because of the plane. Rachel seems to be feeling guilty.
Tina apologizes to Kurt and Blaine for how she acted. Kurt assures her that he and Blaine are just friends.
Marley thanks Ryder for all the gifts he suggested to Jake. He leans in and kisses her, then quickly apologizes. She rushes off awkwardly.
Finn implores Will not to give up on Emma. He pledges to help him win nationals and get his wife. They shake on it and Will thanks him.
Betty apologizes to Artie for how she acted at the wedding. He asks her out on a date.
The Glee kids sing "Anything Could Happen".
The episode ends with Rachel taking a pregnancy test and looking concerned.