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.
Sure enough, Joe is feeling better with the treatment. Foreman checks him out to find how much he's improved, but his cold attitude toward Joe makes Joe suspect that Foreman has a problem with the police. Chase comes in with a chest X-ray that shows that the cop's lungs are, indeed, looking better. Foreman comes over to the other side of the bed. Joe addresses Foreman, but he's looking at where Foreman was standing before, not where he is now. Joe asks a few nervous questions about whether Foreman "found anything" at his apartment. Foreman turns the X-ray display around and tells the cop some more stuff about his lungs, pointing to areas of the X-ray display. Joe doesn't notice the X-ray. Foreman waves a hand in front of Joe's face, which he probably just should have done in the first place, and again, the cop doesn't see it. Which is good, because he probably wouldn't like seeing Foreman and Chase's resulting "oh, shit" faces.