Why is it that whenever a new kid shows up in young-adult novels, things get majorly shaken up? In this case, it's the arrival of the brace-faced, would-be genius Marti that begins to reform the fabric of Madmen society.
As you've probably figured out, Marti wouldn't be a Madman if she didn't have some major dysfunction going on in her life. For one thing, her parents are an unlikely marriage of a pot-smoking party girl and a physics professor who formerly worked as an atomic scientist. According to Marti's dad, being a genius runs in the family, and he's bent on making sure his daughter follows in his footsteps. By the way, did you notice that his name is Martin and hers is Martinella? Talk about trying to create your child in your own image.
Marti's been to dozens of schools in her life because her dad pulls her out every time she doesn't get genius-level test scores or grades. As a result, she's never had friends or anything resembling a normal life. "She couldn't remember a single interesting thing that had ever happened to her," (9.102) Karl says.
Maybe it's that she's had to defend herself all her life against her father, but Marti's also a fighter. She knows she's different, both in terms of her troubled life and her nerd-girl appearance, but rather than shrink from it the way the rest of the Madmen do, she owns up to it. "Marti wasn't the type to give up without a fight," Karl describes during the Huck Finn incident in Gratz's class, "especially not if she was very afraid—some people are like that. They lean into the fear" (15.116). You go, girl.
It's this fearlessness that leads Marti to be the catalyst for change in the Madman Underground. In particular, she drives the group out of the Underground and into the light. When Karl discovers the whole group sitting together at Philbin's while he's working on Friday night, Bonny spills how they decided to be friends in public rather than hiding from it: "Marti said everyone really knows who the therapy kids are anyway. I mean, we know who's in the other groups, you know? And we all get teased […] Marti said, why not just be friends in public?" (21.73). Good point, Marti.
Ultimately, Marti becomes more than just a friend for Karl—she's the force that declares it okay for the Madmen to stop hiding from each other and ends all executions of Operation Be Normal. While Karl and the others have previously been ashamed of who they are, she has embraced her identity, and in doing so, gives them an example for how to do the same thing.