Chase and Cameron go to investigate the one link they've found between the two sick kids: the school bus. The driver is hesitant to let them in, but changes his mind when they tell him what's at stake.
Margo bitches to Foreman that House said "horrible" things to her in order to make her agree to give her son medicine that turned out to be wrong. Foreman says that House thought it was the right medication at the time and wanted to do whatever it took to get it to his patient. Margo says that if they had listened to her assertion that Matt had thrown the pesticide out, they would have known better. Foreman says that House just assumed that Margo was wrong, which patients and their families usually are. "You're just as pompous and superior as he is!" Margo exclaims. Foreman is devastated at the comparison. Hee hee hee.
The bus driver tells Cameron and Chase the exact location where Matt and Chi sit on his school bus. Either that bus has assigned seating, or being OCD about where you sit is one of the first symptoms of the mystery poisoning. Driver says he noticed a rash in his groin area recently and is worried that he, too, has been affected by the poison. Cameron reassures him that groin rashes are not a symptom. Chase says that being obnoxious isn't one either, so the driver is safe. Oh, stop trying to be House, Chase! Only Foreman can do that. Chase checks out the inside of the bus while Cameron asks the driver if there was any spraying going on on his bus route. Driver says there was a truck spraying some funny-smelling chemicals.
Speaking of funny, House goes to check on his elderly, lustful patient, and she is delighted to see him. The son isn't, so House asks him to take his annoying self out of the room. Grandma Sex apologizes for her son's crankiness and says she would like him to stay in the room. House asks Grandma Sex if she's had sex recently. Grandma says she's hit a "dry spell." A fifteen-year-long dry spell. I wish she hadn't used the word "dry" there. Ew. Ew. Ew. Son says that the dry spell is actually just eight years long, since that was when his father died. What are you even still doing in the room, Son? The second someone asks my mom about her sexual activity is the second I am out of the room, down the elevator, out of the building, into the parking garage, and driving away until my gas tank runs out. Grandma Sex points out that just because her husband was alive doesn't mean he was doin' it. House says that Grandma Sex has got herself some syphilis. Son is aghast, like after hearing all about his mother's sexual fantasies and desires, THAT would be the thing he had a problem with. Grandma Sex doesn't look all that surprised by the diagnosis, which House notices. She says they used to call it "Cupid's Disease" back in the days when soda used to cost a nickel and penny candy really did cost a penny. She's had it since Prom Night 1939 (soon-to-be-regretted theme: We Love the Germans!). I wonder if Grandma Sex and her prom date did it to then-top twenty hit "Beer Barrel Polka," a bit of trivia that just makes me all the happier that I wasn't born sixty years ago. Son says he always thought his father was Grandma Sex's first love, like, how to you get to be his age and still entertain the notion that your parents aren't human like the rest of us? Grandma Sex says he was, but that doesn't mean she didn't have screw around before she met him. Son looks over at House, who just shrugs and reconsiders his position on restricting patient contact, since this is even more entertaining than General Hospital. Grandma Sex says she was treated for the syphilis, which House says only served to suppress the disease for the last sixty years. Now it's back and eating her brain cells. "Oh! That's revolting," Grandma Sex says. I see the brain damage has spread to whatever part of the cerebral cortex monitors the correct use of the word "revolting," which I think better describes discussing your high-school backseat prom sex in front of your son. House agrees, sort of; he thinks chlamydia-caused "seepage" is much more revolting than syphilitic brain damage. He welcomes Grandma Sex to the new century with a prescription for penicillin. She should be feeling better in two weeks. "I guess for the next two weeks, I'd better practice safe sex!" says Grandma Sex, who is a lot more hopeful than you'd expect someone in the fifteenth year of her dry spell to be.