House finishes an ultrasound and tells the patient that she is not pregnant. The patient says she already knew that, and apparently House has, now for the second episode in a row, insisted that one of his clinic patients was pregnant despite her insistence that she wasn't and would probably know better than he. The patient wants to know why, if she's not pregnant, she's spotting. House says it's because she had a miscarriage, unsurprisingly delivering the news in a less-than-sympathetic manner. The patient claims that's impossible, since she hasn't had sex since her divorce a year ago. So either her miscarriage is taking its sweet time carrying itself outta there, or, as House suggests, the patient should think about starting her own religion. Although I have to imagine that if the Conception were that Immaculate, it wouldn't have, you know, ended like that.
Cuddy intercepts House as he leaves the exam room. She sternly orders him into her office. House swings his cane around and tells a nearby nurse that Cuddy loves his "hard wood." The nurse, who is hilariously not shocked by this, simply glares disapprovingly.
In her office, Cuddy informs House that he will not be doing a brain biopsy on a U.S. Senator because brain biopsies are dangerous. House says that brain tumors can be kind of dangerous, too, but this is all beside the point since this is his case and therefore his call. Cuddy disagrees. House asks if she's trying to pull rank on him. Cuddy says it isn't her call, either.
The two flank the Senator's bed and debate the pros and cons of a brain biopsy. The pros are that they can find out what that mark on the MRI was and, they hope, treat the Senator for it. The cons are that brain biopsies involve sticking needles into the brain and really shouldn't be done unless they're absolutely necessary, and Cuddy doesn't think a spot on an MRI qualifies. The Senator, who is now stuttering as his brain problems advance, just wants to know which course of action will get him the most votes. This is why House normally doesn't consult with his patients before choosing their course of treatment.
Since dying from a mysterious illness loses more elections than possible brain damage, the Senator chooses to have the brain biopsy. There is drilling. Then House, Foreman, Wilson, and Cuddy check out the results. Wilson looks in the microscope and reports that there is no tumor, and Cuddy is slightly annoyed that they did a brain biopsy for no reason. House tells her to hold her brain-biopsy-hating horses, since Wilson is making a funny face. Indeed, he looks up and says that the Senator has a touch of toxoplasmosis. The spot on the MRI was a toxoplasmosis lesion. And that means AIDS. While this could affect the Senator's election chances, it doesn't rule out a very short-lived career as a talk-show host. Every cloud has a silver lining.