Shawn and Gus recount their adventure in London through a "Guy Ritchie" style voice-over (replete with a bad British accent from Shawn). It is revealed that Gus is in London for a Harry Potter convention called "Pottercon" and that Shawn has been summoned by Interpol to help on an undercover sting.
Winston, a mid-level investigator at Interpol, explains that their inside guy on the sting, an American driver, was arrested and can no longer be a part of the operation. Then Winston tells Shawn that he bears a striking resemblance to the driver and that Interpol needs Shawn to go undercover as him. They tell Shawn that their boss Royston Staley sent for him. Shawn and Gus go to meet Royston and are shocked to see that Royston is actually Pierre Despereaux.
Shawn and Gus are confused as to how he infiltrated Interpol. Despereaux, a.k.a Royston Staley, explains that ten years ago, he was an employee at Interpol who was given a mission to go undercover as a man named "Pierre Despereaux." Years later, after the completion of his mission, he returned to Interpol to create a different undercover mission, a mission that would crack the ranks of Interpol's most wanted criminal, Ronnie Ives. Ives is a ruthless criminal who never uses the same crew twice on any heist and is exceptionally good at evading authorities. Interpol knows the only way to catch him is with someone on the inside. Shawn is now their inside guy, the soon to be getaway driver for Ives.
Time is of the essence, so Despereaux starts training Shawn for the mission. Despereaux tells Shawn to memorize everything in his look-alike's file so that when Shawn goes undercover, Ronnie will believe he's the same guy he originally hired to be his driver. Unfortunately, Shawn has trouble with this, so Despereaux decides to hook Shawn up with an earpiece for when he's in the field.
Dressed and ready for the mission, Shawn meets with Ives and his crew at "The Bloody Bucket," a local pub. Despereaux is outside stationed in a surveillance van guiding Shawn on the mission through Shawn's earpiece. Despereaux tells Shawn his main goal is to find out where and when the next heist is going to be and get out. Before Shawn can do this, Ives reveals there is a traitor in their midst and that the job is off. Shawn panics, thinking it's him. Tension rises, but Ives calls someone else's name in the group. Ives outs him as a traitor and promptly murders him. Ives returns to the meeting area and Shawn convinces him to go through with the job. Concerned they are one person short, Shawn says that he knows a guy named "The Wizard" who would be perfect for the mission. Shawn goes outside and drags Gus in, who is wearing Harry Potter-themed wizard attire, complete with a magic wand. Ives agrees to bring on Gus as their new explosives expert. Gus tells everyone to refer to him as "The Wiz."
We follow the crew, Ronnie Ives, Dierdre, 'Arry, Shawn, and Gus, to a warehouse. Ronnie says that Shawn and "The Wiz" need to prove themselves worthy for the mission before they begin. Shawn is given a driving test and fails miserably, hitting every traffic cone in his path. Ives misinterprets this as useful fearlessness and keeps Shawn on the job. Gus then has to prove his talents. When Gus uses his magic props and nothing happens, he is almost exposed, but Despereaux blows up a nearby trash can to keep Gus' cover alive. Shawn and Gus are now accepted as members of the crew.
Shawn and Gus head back to Interpol to touch base with Despereaux, but they're told he's in a meeting. They run into Winston instead and let him know they were able to steal Ronnie's key card to his office. In the same conversation with Winston, Shawn and Gus find out that no one at the office knows much about Despereaux and that he started working there when there was a staff turnover. Also, no one has met the man who supposedly hired Despereaux, Wim Stuyvesant. Shawn becomes suspicious. He calls Lassiter to get a background check on the two names. After performing a little research, Lassiter reveals that no one with those names exists. Despereaux is setting them up and trying to find out where Ives' next job is so Despereaux can get in on the action. A disappointed Shawn tells Winston the bad news.
Shawn and Gus head over to Ives' office with his keycard to see what they can find. There, they find an English genealogy book and a few related documents, then discover that Ives' father recently passed away. Shawn also finds a note in the trashcan with the location for a security firm for the royals. Shawn then remembers that the mission involves robbing a house, so he puts two and two together and realizes Ives is going to rob one of the royal residences. Shawn and Gus head to the door, only to be stopped by 'Arry at gunpoint. He negotiates their share of the heist for not telling Ives about their break in.
Shawn and Gus head to Interpol to talk to Winston. Winston is looking up all the royal residences and is having trouble narrowing down which one is going to be robbed. Shawn says he knows that the house has a kitchen with a south-facing window. Just then, Despereaux walks in, and demands Shawn and Gus come to his office. While they are following him, Shawn gets a text from Ives that says: "Warehouse. Now." Shawn and Gus jet out of Interpol and head to the warehouse. They tell Winston to keep Despereaux in the dark about their plan as they leave.
As they arrive at the warehouse, they see everyone standing outside next to a van. It's time for the job, and Shawn is thrown the keys to drive. Ives tells him they have to pick up one more replacement member after Ives pegs 'Arry as a rat. Ronnie throws 'Arry out of the speeding van, then reveals that the new member of the team is none other than Despereaux.
The crew pulls up in front of a gated manor. As they approach the house, Despereaux tells Shawn and Gus how Winston kept info from him and that's why he had to bring back his alter-ego Despereaux. Just then, Shawn gets a call from Lassiter who tells him that he was mistaken before, and that Wim Stuyvesant is a real person, but he was erased by someone who has high clearance levels within the organization. Armed with this information, Shawn realizes that Royston Staley is also a real person.
Shawn and Gus realize they have to go through with the job. They are instructed to head to the upstairs bedroom to blow open the safe. The two of them head up there with the hopes of stalling long enough for police backup to arrive. When Shawn and Gus enter the room, they realize it already looks like it's been robbed. There also isn't a safe. After looking around a little more, they find the dead body of Calvin Dorchester. The duo then understands that they've been set-up; the job was an assassination, not a heist. As they turn to leave, Dierdre is there, ready to kill them as planned. As she reveals how they were set-up, Shawn scans the room and puts some pieces together, remembering the things he found out while at Ives' office. Ives put this job together as revenge on Dorchester, who cheated his late father out of the royal life that was rightfully his. Ronnie enters behind Dierdre to finish off Shawn and Gus. Just as it seems this is the end, Despereaux swoops in and disarms both Dierdre and Ives just as backup arrives on site. Shawn and Gus are saved, and they realize that Despereaux's real identity really is Royston Staley. Just as they are walking out of the house, Despereaux is summoned by Wim Stuyvesant. The Interpol officers present are shocked to finally see Wim in the flesh.
Back at Interpol, Royston (Despereaux) is packing his things. Wim has suspended him from Interpol for letting the case get out of hand. He leaves, and Shawn and Gus ready themselves for their journey back to Santa Barbara.
Before they head to the airport, Shawn and Gus stop for a drink at The Bloody Bucket pub. While there, they catch a glimpse of Wim Stuyvesant dressed as a homeless person. This leads them to believe that Despereaux hired this homeless man to play the part of Wim Stuyvesant in order to make Interpol believe Wim was a real person all along; which then leads them to believe that Despereaux was the true mastermind behind everything. And once again Shawn and Gus are pretty much convinced that Despereaux set them up.
- Executive Producer Kelly Kulchak is a huge Harry Potter fan.
- During the story development process, the writers would often pitch lines and jokes for the episode in British accents.
- Kell Cahoon, co-writer of the episode, does a great Vinnie Jones impression.
- The Psych writers watched a lot of British gangster movies in preparation for developing the episode.
- Most of the episode was shot in Gastown, a national historic site in Vancouver, British Columbia that bears a resemblance to London, England. This is referenced by Gus' line that they might as well have gone to British Columbia.
- This is the fourth Psych episode Cary Elwes appeared in as Pierre Despereaux.
- With this episode, Carlton Lassiter becomes the only character beside Shawn and Gus who has appeared in every story of the show.
- In this episode, Shawn and Gus suspect Despereaux is impersonating an Interpol agent. In Season 1's episode "Speak Now or Forever Hold Your Piece", Shawn impersonated an Interpol agent.
- The episode title is a reference to both the 1998 film Lock, Stock and Two Smoking Barrels (which starred guest actor Vinnie Jones), as well as the novel and film Harry Potter and the Goblet of Fire.
The gallery for Lock, Stock, Some Smoking Barrels and Burton Guster's Goblet of Fire can be found here.