The next day, House enters Mark's room and asks if he can talk to Stacy. His hangover has given him a better attitude, it seems. Mark assents. House and Stacy walk down the hall, and House tries to be the Bigger Man by saying that Mark seems like a good guy. Stacy chooses not to accept House's attempt to do the right thing, and snots that House doesn't know anything about Mark. House says he knows Mark took Stacy to Paris, her dream city, and that's good enough for him. Stacy says they've never been to Paris, and that their honeymoon consisted of a night in New York before she returned home to work. HOT! House asks when Mark switched from mountain biking to yoga, and Stacy says it was about the same time he started getting sick. House says they have two more symptoms. I think we can link this all back to yoga, one of the most dangerous of all physical activities. People, I had to WASH MY OWN CLOTHES! And listen to my mother complain about the pain in her back! Oh, how I suffered!

House shows the Cottages Mark's PET brain scans, saying that they tell them everything they need to know. You see, lying takes a lot more brain involvement than telling the truth, and the scan of Mark's brain when he said he and Stacy went to Paris showed minimal involvement, meaning he thinks it really happened. And it didn't.

"DELUSIONS," House writes on the whiteboard in big letters. He thinks Mark has Acute Intermittent Porphyria, which can only be diagnosed when the patient is in the middle of an attack. Chase says that there are other symptoms, like light sensitivity, and House points out that Mark recently gave up the outdoor activity of mountain biking for indoor yoga. He tells them to start Mark on glucose and hematin. Cameron points out that if House is wrong, the hematin will kill Mark immediately, meaning that this time, the guess treatment is more dangerous than doing nothing. They'll need to confirm the diagnosis, but the only way to do that is to get a urine sample during an attack, and there's no way to predict when the attack will happen. "Sure, there is!" says House. Uh oh.