A man, Bert Vesky, cleans up a blood-covered apartment. His cell phone buzzes and Bert answers it, and tells his wife Diane that his meeting is running late and he'll meet her at the restaurant. Once he hangs up, Officer Smith comes in and tells him to get back to work.
Later, Bert meets Diane at a restaurant and the waiter serves live sushi. Bert eats it despite Diane's protestations and then offers her a toast. As he starts to talk about the day he met her, he chokes and watches as a rash spreads across his hand.
Cuddy is leaving when she notices House slipping out in the elevator. She tracks him down and insists that he goes to the charity award dinner the coming Friday where she's getting an award. House finally admits that he already RSVPed despite his protestations, and considers it foreplay.
House arrives in the conference room as Foreman complains that his roommate Taub is wearing one of his ties. House asks how Bert could have had an allergic reaction when all the tests were negative. When he points out that Bert is an executive, Masters points out that the calluses on his hands means that he's lying. House hugs her and says she's finally grown up, until she admits she hasn't told Bert he's a liar. He tells her to go ahead and Masters wonders how to break the news to him. House tells her to pick one of her teammates to go with her. She takes Chase and tries to get Diane out of the room, and Chase finally steps in and says they want to ask Bert about bowel movements. Once she leaves, Bert asks them not to tell Diane, and Chase immediately promises. Bert says that he lost everything in the recession, and Diane has no idea. Now he works as a cleaner on industrial jobs and crime scenes.
Masters and Chase report to House, and Foreman figures that Bert might have picked up something from the crime scene. House tells them to check Bert's old office, where he goes to hang out to convince his wife he's still working, while he goes to see Cuddy and convince her to get the autopsy report on the victim at the crime scene from the police. As House steals a sandwich from a patient's tray, Wilson asks House why he's going to the charity gala, and doesn't believe he's claim that he's being nice. He bets $100 that House won't show up. House points out that Wilson is giving him a selfish incentive to show up, but Wilson doubles the bet. At that, House realizes that Cuddy is paying Wilson to bet to make sure House is there.
Taub and Foreman Taub go to Bert's old office and haggle about the tie. Foreman finds a bottle of unprescribed Vicodin, while Taub finds a closet filled with boric acid containers. When they get word, Masters and Chase tell Bert that they suspect contamination from the acid, but Bert's temperature spikes and they try to bring it down before it causes permanent brain damage. Once they succeed, they report to House and confirm that there was no boric acid on Bert. The autopsy report is negative for communicable diseases. House wants the Vicodin, to supposedly confirm what it really is. He samples it and declares that it's real, but notes that it doesn't cause Bert's symptoms. House suggests meningococcemia and orders a lumbar puncture to confirm, and find out what else Bert is lying about.
As Chase prepares the lumbar puncture, he and Masters say they need the complete truth. He admits that he took the Vicodin to hide the pain rather than give away his scheme to Diane, and then tells them that he maxed out the credits cards and put a double mortgage on their home. As they begin the procedure, Bert asks them what they did when they had problems in their relationship. Chase admits that he told the truth, eventually, and it didn't work out well.
House goes to Wilson and asks him whether he has to donate money to the charity. He wants to know a way to have fun, but Wilson tells him to just show up and behave. He wonders if House plans to sabotage it and ruin the event for Cuddy, and House leaves.
As the team runs tests, Taub suggests that he and Foreman get dinner. When Foreman says he has other business, Taub pursues the matter and Foreman finally admits that he's on a date. Meanwhile, Masters complains to Chase that he's mad at her because she's a woman and is offended that he's okay with Bert lying to his wife. The tests prove negative for meningococcemia, but Bert's legs start to swell up. The team restores his circulation before infection sets in, and suspect serum sickness. House asks the others who is going to the charity ball, and insists that everyone goes there whether they already planned to or not. Foreman figures that he wants more witnesses for when he screws it up for Cuddy. House tells them to treat for serum sickness with steroids and leaves.
In the locker room, Taub comments that Foreman had to cancel his date, and Foreman finds his attitude annoying. Taub finally tells Foreman that Rachel is meeting with her online "friend," and Foreman finally takes pity on him. Taub offers to make dinner, and afterward they end up playing video games, and Foreman realizes that Taub is letting him win. Taub tells him that he has to learn to lighten up, and Foreman notes that Taub is the last person to give advice on relationships. As he points out that Taub screwed up his relationships, they both start feeling stomach pains.
Bert hits Diane and locks himself in the bathroom. As they try to get the door open, Bert looks in the mirror and starts hallucinating blood and the walls closing in. Once the team stabilizes him, they go back into differential. Once the steroids they gave him cleared his system, the hallucinations stop. Foreman is still feeling stomach pains, and claims that Taub tried to kill him. He runs off to the bathroom and Taub quickly goes to "check on him." They both go to the restroom and House takes Masters and Chase in to continue the differential. Chase suggests a fungal infection, and Masters notes that the saline they used could conceal it on a test. House orders a new round of tests, and tells them to check Diane as well.
As Masters and Chase run the tests, Masters points out that if Bert had been honest, they might have caught it sooner. Chase objects, insisting it isn't relevant. Diane comes in and they explain that they're treating Bert for fungal infection, and they need to treat her as well. When she wonders how Bert could have got a fungal infection, Chase tries to cover. However, Bert finally speaks up and asks to speak to Diane in private.
Wilson is meeting with a patient when he hears music coming from House's office. He investigates and discovers that his friend has brought in a mariachi band. House explains that he's auditioning bands for the charity ball, and insists that he's doing it for Cuddy's benefit. House ignores Wilson and has the band continue playing.
Masters and Chase watch as Bert talks to Diane, and Masters insists that it's for the best. When Diane comes out, she realizes that everyone knows except her, and tells them to tell Bert that she's done with her husband. Bert's fever goes up and he goes deaf. The new tests prove negative for fungus and spores, and Chase and Masters start arguing over the diagnosis. House wants to hear from Foreman and Taub, and Foreman suggests an infection that has reached Bert's brain. As House agrees and tells them to test for a tumor, Taub tells Foreman that he's moving out. Foreman just tells him to hand over his keys and leave.
Wilson and Cuddy meet for lunch and Cuddy admits that she figures that House will do something to ruin it. When Wilson suggests that House might consider a mariachi band, Cuddy admits that it's a good idea and she's been trying to get the hospital to pay for a band.
As Masters and Chase run tests in the MRI, Bert asks if Diane is coming back. Masters tells her that she hasn't yet, and Chase tells her to improve her bedside manner. Bert goes into a coma. The team believes that it's a tumor and House says that they need to do chemo, even though they can't confirm he has a tumor, and tells Masters to get Diane to give consent. When she objects, House tells her that it's time for her to handle things on her own. As she prepares to tell Diane, Chase comes by to watch. Masters wonders if she likes him, and admits that she's put friendships on hold to further her career. But now she can't even get a date to the ball. As Diane arrives, Chase tells Masters to be honest, but side with hope. Masters tells her the truth but says that there's still hope, and Diane asks if Bert can still hear her, even in a coma. Masters lies and says that his hearing is fine, and Diane apologizes to Bert for what she said earlier. Diane then says that she has a secret of her own, and was going to tell him at the restaurant that she's pregnant. As she talks, the rash spreads over Bert's face.
Back in differential, House tries to figure out why the rash came back, and figures that they did something to trigger it. They try to figure the connection between the crime scene and the MRI, since both incidents occurred two hours before the rash. When Masters points out that the MRI room is cold, House tells them that he has CAPS, a genetic disorder causing Muckle-Wells Syndrome. They can treat with rilonacept, and House comments that Bert can go back to lying to his wife and children.
As Maters and Chase go back to Bert's room, he seizes. Masters tries to revive him but Chase finally stops her when it's clear it won't do any good.
Later, Wilson finds House in his office and asks if he's okay. House claims that he's happy that he solved the case, but has accepted he can't save everyone. Wilson apologizes, admitting that he's grown bitter and cynical. He tells House to go home and change for the party.
In the locker room, Foreman tells Taub that he doesn't have to move out, and he doesn't want to end up lonely like House. Taub admits that Foreman was right about what he said, and they shake hands.
In the lobby, Chase finds Masters waiting to get a ride with Foreman and Taub. Chase admits that he's going alone as well. The others arrive and they head out.
House is drinking in a bar when his phone rings. He ignores it and Wilson comes in, and House admits that he's drinking because he blames himself for all of the patients that he's lost. Wilson points out that it will happen again, and House wonders why, and then says that love and happiness are distractions. All his relationship with Cuddy has done for him is make him a worse doctor. He asks Wilson how Cuddy is, and Wilson says that Cuddy is worried and angry that that House didn't show up. House says he needs to tell Cuddy the truth, but Wilson takes his keys and tells him he's not talking to Cuddy when he's drunk. House walks away.
Cuddy wakes up when House knocks on her door. He tells her that they need to talk, but she tells him to go home. House refuses and tells her to sit down for what he has to say. He then announces that being in love makes him a crappy doctor. Cuddy tells him that he's too drunk to end the relationship, but House blames Cuddy... while admitting that she's totally worth it. He sits down next to her and says that he'd always choose Cuddy, and always will. She tells him to go to sleep.