Lelouch confronts Prince Clovis and eventually kills him.  Later back at school, Lelouch learns that the girl that was with the rebels is in his class.  Her name is Kallen Stadtfeld.  He uses the Geass on her to learn more about her involvement with the rebels.  When he tries to use it a second time to warn her not to say anything about Shinjuku he learns that the Geass doesn't appear to work twice on the same person.