The world may never know. Add it to the list of unsolvable mysteries, like how many licks it takes to get to the center of the Tootsie Pop.
Denny's parents don't seem like the warm and fuzzy type, mostly because they've been estranged from their son since he finished high school. When we meet them, they're old and frail, more snapshots of strangers than people who seem to have a real emotional connection to Denny.
Still, they show up with their suitcases and a wad of cash to help Denny out of his financial and emotional crisis, and it could not have come at a better time.
It turns out that Denny and his parents are estranged because Denny wouldn't take over their farm after high school. He high-tailed it out of his hometown as fast as he could—which, for a semi-professional racecar driver, had to have been pretty fast—and set off to make a life for himself. His parents decided shortly after that to have nothing to do with him, and it has taken years of calls and asking, talking, and then begging for them to come around.
In fact, it takes Denny telling them that he's going to lose Zoë if he doesn't figure something out for them to really come around. So thanks, Zoë, we guess, for bringing families together.