Chase informs Joe, who's still laughing and having the greatest time ever while he's wheeled down the hallway, that his bloodwork showed low-level carbon monoxide poisoning. Oh, so I guess the case is closed, then. That certainly was fast! Especially since this is a two-parter! What will they do for the remaining hour and forty-five minutes? Maybe Cameron will take some more meth and be awesome again. Cameron asks Joe whether he lives near a gas supply, and Joe answers that the only one he can think of is himself after he's had a few burritos. Cameron does not appreciate his humor. Joe says he keeps a "pretty clean" home.
Cut to Foreman in a decidedly unclean home. There are pots and pans piled on the counters with leftovers on them. The fridge is disgusting. The bathroom looks surprisingly clean. Foreman takes samples of everything. He even takes a trip to Joe's balcony area.
Chase and Cameron set Joe up in an oxygen chamber. They give him a button to press if he needs assistance in there, but Joe just keeps pressing it like he's in an SNL "Celebrity Jeopardy!" sketch. Finally, Chase confiscates it. Suddenly, Joe's arm has a muscle contracture, which Chase ascribes to the carbon monoxide.
Meanwhile, Foreman has found a secret greenhouse on Joe's balcony. He's got one hell of a set-up there, with lights and irrigation and everything! And it's all to grow one plant: marijuana. So much marijuana. More marijuana than anyone could ever possibly need.
Meanwhile, House isn't making any friends at Joe's precinct, where Joe's co-workers seem strangely unconcerned about their colleague. The only person who seems to welcome House's presence is a transvestite who gives him a flirty smile that House returns with an uneasy greeting. House tells an impatient cop that he isn't actually there to check Joe's workplace for toxins, since he figures that if there were any, half of the force would be sick like Joe. Instead, House has a bag full of speeding tickets that he'd love someone to take care of for him. "I'll see what we can do," the cop promises, looking like all she's going to do is wipe her ass with them. Hopefully, she'll be able to remove that stick she's got lodged up there while she's at it. Just then, House hears someone cough, and his attention is directed towards an air-conditioning unit that the cougher is sitting right next to. The sick cop sits in the same area.
Foreman and House reach PPTH at the same time. Foreman thinks he's solved the case: all of the cop's symptoms (except, I'd assume, that clear tox screen) can be explained by the marijuana use. But House thinks they're looking at Legionnaires Disease, judging by the "rancid, unchanged" water he saw in that air-conditioning unit. And House is the boss, so they'll be treating Joe for Legionnaires.