The police have called Shawn and Gus down to the television studio, where there has been a murder on the set of the telenovela Explosion Gigantesca de Romance, Gus' favorite soap opera. But when they get to the set, Lassiter says Juliet jumped the gun calling them and the case is open and shut, in fact the whole thing was caught on tape. One of the actors, Jorge Gama-Lobo, stabbed the victim during one of the scenes. But Jorge insists someone switched the prop knife for a real one without his knowledge. Shawn looks around and sees a long hair on the murder weapon. He also watches playback of the incident and can see the genuine surprise on Jorge's face. He claims Jorge is innocent. Vick tell him he's not under arrest yet, he's just been temporarily suspended from the show. Gus can't believe it. Jorge's character is in the middle of an important love triangle with the character Corrine. Shawn tells Vick about the hair on the knife that clearly wasn't Jorge's and asks for one day to investigate at the show. She agrees.
Shawn is as happy as Gus is to be on the set. Craft services means free food all the time. They speak with Lance Rothstein, the head writer, who tells them he knows Jorge is innocent too, and he's not too comfortable having a murderer running around his set. He tells them he doesn't have time to speak now, but they can find Jorge in his dressing room. His life is this show and he won't go home. They go to see Jorge, who is so depressed he can't even eat his favorite meatballs from craft services, even though Kelly, the woman who runs it, was nice enough to bring some by. Shawn spots signs of a struggle in his dressing room and Jorge tells them it was Quintessa Gabriel , the actress who plays Corrine on the show. She is a horrible diva and she hates him.
They track down Quintessa, and, as Gus tries to grab a strand of her hair to compare to the one on the knife, Shawn questions her and figures out she was having an affair with the victim. She storms off in a huff before Gus can get the sample. Shawn says they'll get it later and tells Gus to question the prop guy while he sees if Lance is now free to talk. The prop guy, Gelbart, tells Gus Jorge would never have known the knives were switched as the prop is made to feel genuine. Shawn meanwhile finds Lance on set filming a scene, trying to get a decent performance out of the actor playing a delivery guy. When Shawn makes some suggestions, Lance gets an idea. So when Gus tracks him down to tell him the knife changed hands six times before getting on stage, he finds Shawn in the middle of a scene as "Chad," the new delivery man.
Back at the police station, Lassiter and Juliet are questioning Anita, one of the actresses, who tells them that Lance and the writers have brilliant minds for coming up with creative deaths. When Lassiter gets to the set, Shawn is just finishing up a scene with Quintessa, where he has just nabbed one of her hairs. Lassiter is stunned as Shawn is brought special food by Kelly, who calls him Chad. Shawn gives him Quintessa's hair, but he blows it into the wind, telling him that the hair on the knife was synthetic from a wig. Lassiter continues to the writers' room and confiscates all scripts and written material as evidence. Back at the station, he gets a call that Jorge tried to kill himself and left a note confessing to the murder. They rush to the hospital, they find Shawn and Gus already there, listed as friends and family. As the cops get kicked out, Shawn notices a synthetic hair on Jorge. This wasn't suicide. The same person tried to kill him, too.
Meanwhile, the cops discover that the note wasn't a suicide note either. It came directly from a script written by Lance nine years ago. The cops arrest Lance but Shawn knows he has no motive. Henry comes to visit Shawn at the one of the few real jobs he's ever had. It turns out Henry is a fan of the show as well, and starts berating Shawn for all the bad things his character has done on the show. Shawn realizes that if his dad can blur the lines of reality, someone else could too, like a crazed fan. Shawn has an idea. He and Gus visit Lance in jail and tell him that the murderer is targeting actors whose characters have wronged Corrine in some way, and a fan is killing to protect her. He needs Lance to write a scene where Chad goes after Corrine in order to draw the killer out, and then Corrine should try to kill Chad so they can catch the culprit as he tries to switch the weapons again. The only problem is, they are running behind on the show because of all the behind-the-scenes drama and they will have to shoot everything live for Friday's show. But when the time comes to shoot the scene, Quintessa starts improvising and there is no time to check the weapon before it goes in front of the camera. Luckily, before she can fire off a shot, Shawn sees Kelly off-screen and notices indentations on her hairline made from wig clips and realizes she's the killer. She had access to the props and the scripts; she poisoned Jorge's meatballs and is obsessed with the character Corrine. Kelly is arrested and Chad is killed off the show, but as everyone who watches a soap opera knows, that doesn't means he's gone for good.
- The telenovela nature of the setting is alluded to in the use of 'Homicidio', but the title in essence is drawn from the famous filming cue sequence, 'Lights! Camera! Action!', which it has been suggested was first used by D. W. Griffith.
- Shawn struggles with his lack of Spanish skills in this episode. In real life, the actor James Roday is half Mexican (his name is actually James Rodriguez) and speaks at least semi-fluent Spanish.
Gus: This whole thing is starting to feel like a real soap opera to me. I can't believe he would try to take his own life.
Shawn: Unless he was wearing a wig, he didn't. Someone else did.
[dramatic music swells]
Gus: What? I don't get it.
Shawn: Really? I thought I wrapped it up so nicely for you just now. It felt really good. It was organic.
[picks something out of Jorge's hair]
Shawn: Synthetic hair... just like the one found on the knife.
[dramatic music swells]
Shawn: Dude! It means the same person was there when Jorge tried to "kill himself". He wasn't alone.
[dramatic music swells]
Gus: So, wait... you're saying he didn't try to kill himself?
Shawn: [sighs] I can't do this.
Gus: You're not being clear, Shawn.
Shawn: Come on, dude! I gave it to you three different ways.
The gallery for Lights, Camera... Homicidio can be found here.