Wilson talks to House about all the time he's been spending with Stacy lately, and how House only shows up at the Stacy residence when he knows Mark is out. Wilson thinks Mark might have a problem with that, but House points out that Stacy obviously isn't telling Mark about House's visits because Mark thinks Stacy still has feelings for House because Stacy does, in fact, still have feelings for House. House figures that if Stacy did tell Mark about House, he won't get through the front door tonight. If she hasn't, however...

Cut to House and Stacy in the attic on rat stakeout duty. And just where is Mark supposed to be tonight? At the physio slumber party? House points out that Steve McQueen has cleverly eaten all the cheese around the antibiotics, and Stacy has to admit that Steve McQueen is okay as far as rats go. House says that Steve McQueen is so cool that he even smokes little rat cigarettes, as evidenced by the traces of nasty chemicals House found in Steve's urine. I hope he paid for those tests out of his own pocket, because I'd hate to think of my health insurance rates going up because some doctor was abusing the lab's resources for his own little vanity project. Obviously, Steve isn't the one smoking those cigarettes. House says that Mark should really stop puffing or else risk his AIP coming back. Stacy admits that she's actually the secret smoker, and has been exhaling her fumes in the air vents Steve McQueen frequents in order to hide that fact from Mark. "I always knew," House says. Stacy doesn't believe him until House details exactly when Stacy started smoking (two weeks after House's leg surgery) and what types of cigarettes she preferred. He never told Stacy he knew because the cigarettes allowed him to monitor her "misery level": the more she smoked, the more unhappy she was. You have to resort to things like this when your lover's face is incapable of showing any telling expressions. "I'm sorry you were miserable," he says. "I'm sorry I caused you so much pain," Stacy says. Wow, that scene was almost kind of nice. Their faces get closer and closer and you can almost feel the sexual tension their relationship was supposed to have all along here, and then Steve McQueen gets caught in the humane rat trap and interrupts everything. House glares at Steve and his bad rat timing.