Rebecca is his cousin, albeit a distant cousin. Distant enough for him to feel, well, a little tendresse for her. And if the idea of her prancing around on the stage disgusts him, the idea of her going off with Rimini appalls him. There they discover that Rebecca is in much more trouble than any of them dreamed of before and that Rimini's plans for the rocket fuel could end up changing the very nature of the human race itself. Okay, I'd better stop there.
Some amazing stuff happens, especially to Rebecca.
He's in this, too. Watch his dental work.