At PPTH, Kyle continues to die. His heart rate speeds up, and Chase says it's either an allergic reaction to the diazepam or Kyle's heart is "done."
House asks Dan how the house fire started. Dan says it was Christmas Eve and his wife had taken a sleeping pill and gone to bed, apparently anticipating the loud hoof beats of Santa's reindeer on her roof possibly interrupting her slumber. Kyle was popping popcorn in the fireplace and cruelly trying to burn Santa's ass. Somehow, Kyle knocked some tinder over and it touched the wrapping paper and that was it. Wilson thinks Dan blames his son for the fire and that's why he doesn't want to see him. Dan denies this, saying that Kyle was twelve and it was an accident. That, and someone made a bad decision to wrap the presents with kerosene-soaked paper. Dan says it doesn't matter if he sees his son or not; he couldn't save his wife and now there's nothing he can do to save his son. "Thank you SO MUCH for waking me up!" he shouts.
The sad piano music comes in and House asks Dan how Kyle managed to dislodge the tinder. Dan says Kyle dropped the popcorn tray after complaining that it was too heavy, a complaint that Dan didn't listen to. House asks if his father-in-law's hit and run happened at night. Dan says he thinks so, but he doesn't know why that's important. House asks if the car accident that killed the sister-in-law happened at night. Dan says it did. "Ragged red fiber," House blurts. Myoclonic epilepsy with ragged red fibers, or MERRF, is a rare genetic disease that can only be inherited from the mother. It causes muscle weakness and poor night vision, making its sufferers seem uncoordinated or drunk. Okay, so...all of Dan's in-laws had this undiagnosed condition and Dan just assumed they were all drunks when they weren't? That's...ridiculous. Really, it's just ridiculous. No one assumes someone is an alcoholic because of clumsiness. You assume it because of clumsiness and finding bottles of alcohol in their backpacks.