The episode opens in the jungle somewhere, with a man carrying a gold briefcase that you can just tell is destined to become the episode’s McGuffin. A few seconds later, he’s gunned down by a trio of men led by guest star Vinnie Jones (“Lock, Stock and Two Smoking Barrels”), who takes a cell phone call, tells the person on the other end that he’ll have to call them back, and then calls them “smooshie,” at which his men snicker. As if to buy back his lost masculinity, Jones blasts the corpse at his feet again.
Cut to a dance club, where Sarah and Carina (remember her old friend, introduced briefly in the second season?) are catching up. Telling Sarah that she wants to get out of Burbank as quickly as possible, and asking what’s taking Sarah so long, Carina figures out that Sarah has feelings for Chuck and tells her that she’s broken the “cardinal rule of spying.”
Back at Chuck’s apartment, where Morgan tells Chuck that he’s breaking the cardinal rule of breakups by moping around. He invites Chuck out of their empty apartment to go to a nightclub…which of course turns out to be the same one where Sarah is spending the evening with her friend, who Morgan remembers from their one “date.” While Chuck talks to the girls, Morgan waits at the bar to hear whether or not Carina remembers him. Things get a little hinky, though, when a man comes up from behind Carina and swings her around; by the time she reaches the floor, Carina has put on a large engagement ring and is making smoochie-faces with Vinnie Jones, whom she introduced as her fiancé, Carl. She introduces Chuck as Sarah’s boyfriend, thinking that’s still their cover, and then Chuck has to pretend to have heard of Carl before and make the awkward small talk that such a meeting requires. The pair are preposterously sappy, which makes Chuck and Sarah a little uncomfortable, given the awkwardness between them since Prague. But when Carl turns to leave and Chuck looks after him, he flashes on a long scar on the man’s forearm and realizes that Carl is an arms dealer. Carina laughs him off, telling him that she knows that, and that Carl isn’t her real fiancé but her mark. She reiterates the “spies don’t fall in love” rule and welcomes Chuck and Sarah to their new mission.
Big Mike is wearing a suit and tie when he walks into the Buy More, introducing himself as the once and future manager of the store and saying that he’s taken a business class during his absence, and that he’s no longer going to accept the mediocrity which has always been the hallmark of his reign at the Buy More. A few minutes later, Chuck and Morgan are talking about Carina again, and just as Jeff and Lester join the conversation to tell Morgan that he has no shot with a woman like the one he’s describing, she walks in and whisks Chuck off to Castle.
There, General Beckman is briefing the assembled team-plus-Carina, getting Team Bartowski up to speed on a dangerous weapon that Carl has acquired, and which they’re going to try to intercept before he gets it to his buyer. The plan is for Chuck and Sarah to enter her engagement party as a couple, then sneak off during the toast and steal the case from a heavily-secured vault off Carl’s bedroom. While Chuck is initially hesitant, Sarah assures Carina that Chuck’s “recent training” will make getting into the vault no problem.
Back at the Buy More, Morgan is still trying to prove to Jeff and Lester that he has a shot with Carina. In order to lure her to his bed, the three plan a housewarming party that will give him “home field advantage” when Jeff sneaks his trademark “flammable punch” into the shindig and people start getting sloppy drunk. Morgan decides to go along with it, and guarantees that Carina will show up.
At their apartment later, Morgan is helping Chuck pick out clothes for his “non-date” with Sarah, whom he has told Morgan he’s not back together with. Cut to shots of Sarah and Carina getting into super-hot outfits, complete with hidden knives, after which Carina suggests Chuck’s mother’s charm bracelet for part of Sarah’s ensemble, and Sarah turns it down. Carina asks if she wants to talk about “what happened with him,” and Sarah declines, then also blows off (but doesn’t specifically decline) Carina’s invitation to go on her next mission. Sarah asks Carina if she ever thinks about having a “real” life, and Carina says not.
Morgan and Chuck, though, are talking about Carina back at the apartment, where Morgan convinces Chuck to give her a flier inviting her to the housewarming on the condition that Morgan help him find his missing car keys—which Morgan then pulls out of his own pocket and gives to Chuck.
At the engagement party, while Carina is introducing Carl to her “Uncle” John, Chuck is trying to talk to Sarah, but she keeps trying to avoid his conversation and get on with the mission. When Sarah breaks away from Chuck for a moment, Carina intercepts him and tells him that he has to focus on the mission, and that the reason she’s been cold since Prague is that she’s in love with him. Chuck seems genuinely surprised by this, which is odd since he knew what was happening in Prague, but it’s par for the plot. He chases down Sarah and tries to convince her to talk about what Carina just said, but Sarah tells him they have to stay focused and the pair hurry past the happy, hugging couple and Carina slips them an access card from her fiance’s pocket. After Carl’s toast ends quickly, with Chuck and Sarah still not to the vault yet, she tries to drag out the proceedings first by encouraging him to follow up with a brief toast about their future children, and then by asking Casey to come up and be Uncle John for a few minutes. He babbles on for a while, as Chuck and Sarah come to a vault full of randomly-moving lasers. He begs her to talk so that he cam calm down and flash, and she assures him that as soon as they’ve got the weapon, they can talk about whatever he wants. Once he takes a few deep breaths, he flashes on the security system and does the elaborate, three-minute aerobic avoidance of the laser security system that we’ve all seen a dozen times before in this type of story. Stopping in the door right after he finishes, he declares that now it’s time to talk…but the briefcase in his hand tilts back and catches one of the moving lasers.
Trapped in the vault with gas running while Sarah climbs through the air duct to turn off the poisonous gas, and then, waiting for Carl’s security gunmen to punch in their vault code before dropping out of the duct and beating them down. On the heels of his two-minute monologue confession, almost none of which Sarah heard, Chuck declares his love for Sarah as she opens the vault door and passes out in her arms.
Back at Castle, Sarah is talking to Beckman about their successful mission, and Casey looks at the weapon (it’s small, round, about the diameter of a record album and the thickness of a hardcover book), and asks what it is—when Beckman tells him that’s above his paygrade, and to forget he ever saw it, you just KNOW that this is going to be not just the episode’s MacGuffin, but a good part of the season’s, too. They won’t even let Chuck look at it, which is good because it preserves the possibility that later in the season he can see it for the first time and flash. Beckman says that Carina will bring it back to Langley presently, and when Casey leaves, Carina asks Sarah again if she’s considered joining her on her next mission, to which Sarah responds (as Chuck wakes up, but continues to play possum) that she’s considering it. Calling Beckman back, Sarah requests to be taken off the Intersect project. Beckman tells her that she has to get over whatever personal problems she’s got and be there for Chuck so that he can continue to be an asset. At this point, Sarah catches Chuck watching and tells him it’s time to train; she brings him to a ring where she challenges him to spar with her using bo staffs, and when he can’t immediately flash she becomes agitated and starts disparaging him; when he tells her that he’s too stressed and needs to talk, she tells him that real spies bury their feelings. She keeps trying to force him to flash, putting him in compromising positions with the bo, and he keeps refusing to play along, finally tossing down his staff and telling her that he doesn’t want to hurt her. She sweeps his legs with the bow and, when she has him on the ground, tells him that he can’t hurt her anyway.
Back at the Buy More, Morgan is trying to reach Chuck to ensure Carina’s appearance at the party, while Carina is wandering the aisles with the gold suitcase looking to get it into Chuck’s hands because she’s detected that Carl and his goons are following her. She tells Morgan it’s a laptop that’s to be fixed by Chuck and only Chuck, and Morgan agrees to deliver it on the condition that she attend the party. Carl and the goons intercept her on the way out the door, though, and take her to the car. When Carl accuses her of being a spy, and orchestrating the theft, she denies it, but then he pops a thumb drive into his car’s DVD player, and it shows Chuck, standing just inside the vault door and telling Sarah that he isn’t a “cold-hearted spy” like Carina. Carl takes the flier from Carina and tells her that she’s next, right after he kills Chuck.
That night, the party is raging, with the entire staff of the Buy More and a handful of other mall employees blaring music and mixing Jeff’s highly-flammable punch in the fountain in Chuck’s courtyard. When Carina arrives with carl and his goons in tow, Lester and Jeff mock Morgan for having a “date” arrive to his own party with four other guys, no girls and no beer. At Castle, the team is looking for Carina. They say that the entire American intelligence community is looking for her, and that Chuck should just relax—but a minute later the trusty iPhone rings, and it’s Morgan, calling Chuck for advice on how to handle Carina and her four dates. Chuck tries to nudge Morgan away from danger by telling him that it’s dangerously uncool to become possessive and that he should try to remain aloof and pretend like he doesn’t notice, all the while speaking in overly-articulated sentences so that he can make clear to Casey and Sarah that Carina and the goons are at the apartment.
Worried about the “studs” ruining their chances with the ladies at the party, Jeff and Lester decide to challenge Carl’s goons to a drinking contest so that Jeff, who’s built up a tolerance for his “jail juice,” can be the last man standing. Carina trips a partygoer and takes advantage of the momentary confusion to spike the drinks with a potent depressant, but when the men refuse to drink it, Jeff and Lester merely take a second cup each for themselves and pass out immediately.
In Casey’s apartment, Chuck convinces Sarah and Casey to find the weapon, and use it to negotiate Carina’s return, rather than running out into the party with guns blazing. Just as they come around to the plan, though, Morgan storms into the living room of Chuck’s apartment and, telling her off for bringing dates to his party, and for not remembering his name; he kicks her out of the apartment, and then opens up a footlocker with the gold case in it, tells her that he’s not going to be helping her get her laptop fixed; little does he know, that case is about the only thing he could have done to actually make them leave. As they’re gathering up their belongings and whatnot, though, Casey throws on his bathrobe and runs out to the courtyard, using a garden hose and a lot of anger to disperse Morgan’s party. By the time the baddies exit Chuck’s, offering apologies to the man they think is just a cranky neighbor, he and Sarah have guns drawn; since Chuck won’t take a gun, Sarah gives him a tiki torch and tells him to think of it as a bo for defending himself. As everyone stands in a circle, pointing guns at each other, Chuck tells his friends to drop their weapons; when they do, Carl has his goons lean over to get the guns, and Chuck tosses the lighted tiki torch into the fountain full of Jeff’s punch. The ensuing explosion allows the good guys to take out the goons, leaving Casey and Sarah pointing guns at Carl and Carl pointing it at Carina. Finally, Chuck gives the speech he’d been wanting to give Sarah episode long—but he gives it to Carl, and Carina picks up on the man’s vulnerability, telling him that she really did fall in love with him. When he lowers his gun for a second, she takes him down and reiterates, with Sarah’s help, the “spies don’t fall in love” rule. At Casey’s apartment, Beckman comes over the TV to prevent Chuck opening the case and to tell them that the weapon will remain in Casey’s possession until a team can be sent to pick it up; back at her office, a faceless man with a cigarette lighter is sititng on the corner of her desk; after she’s signed off with the team, she pleads with the man, whom she calls Shaw, to let her “tell them the truth, so they can be prepared,” but he just walks away without a word.
In the courtyard the next morning, Chuck is picking up the garbage from Morgan’s party when Sarah joins him and offers to talk. They share a few words, along with a little metaphor about “the mess you made,” and Sarah leaves just as it looks like she might get drafted into cleaning the courtyard with him. When he calls out to Morgan, whom he still thinks is unconscious, the camera pans to him in his bedroom, having just scored with Carina, who apparently is turned on by Morgan’s being the only man who’s ever stood up to her.
Back at Castle, Carina stops in to tell Sarah she’s sorry she can’t come with her to Saint –Tropez, and to give her the thumb drive with Chuck’s profession of love on it; Sarah finally sits through the whole thing, tears in her eyes, listening to Chuck say what he’s been trying to say to her for two hours.