Marcie is an insecure high school student that has been ignored for years. Because of this she becomes invisible so that she can extract revenge on those who have shunned her. Something interesting about this character is that she doesn't die(like most of the 'bad guys' in other episodes), but is sent to a school where other invisible students attend. At the very end of the episode we see these students turn to a chapter in a text book entitled 'Assassination and Infiltration.' The writers could have used her and this 'school for invisible students' in a later episode but I don't recall them ever doing that.