Mathilde de La Mole dances with a bunch of dudes at the duke's ball to get her mind off Julien. But it doesn't really work. She keeps trying to listen in on Julien's conversation with Count Altamira, which seems to be all about revolution and politics.
All she can think about is how much more interesting he is than the guy she's supposed to marry, a guy named Croisenois.
Mathilde soon realizes that Julien takes away her boredom. That's why she's so interested in him.
The days after the ball, Julien glows with revolutionary passion. Whenever he sees Mathilde around, this glow fades because he's afraid of giving his true thoughts away. All she sees, though, is a drop in his enthusiasm whenever he sees her.
Julien notices that Mathilde is dressed in black as if she's in mourning.
When Mathilde tries to ask him what he's thinking about, he boils over and tells her all the violent, revolutionary thoughts he's been having.
He's so aggressive that he actually scares Mathilde.