Tales of the Madman Underground covers five days in the life of Karl Shoemaker, a high school senior from a small town in western Ohio whose life is coming apart at the seams. Placed in a mandatory therapy group at school for beating up a football player and killing a classmate's pet rabbit in eighth grade (whoa), Karl has been pigeonholed by classmates as a psycho animal murderer, and most of the school is scared of him. While this often comes in handy when dealing with bullies, Karl longs for one school year when he can just be like everyone else.
That's why, on this first day of his senior year, Karl is instituting Operation Be Normal. He has a few objectives in doing this—mainly finding a way to get a ticket out of group therapy and avoiding his best friend and fellow Madman, Paul Knauss. Paul is not only in group therapy but also gay, which wouldn't do much for Karl's new image.
At first, things seem to be going well. Coach Gratz, his ultra-manly English teacher, offers to write him a letter excusing him from therapy because all of the therapy kids are in his first-period class and he doesn't want a chunk of the class missing every other Monday. Karl thinks that from here on out, everything is going to be a breeze—no more therapy will equal no more people seeing him as Karl the Psycho. That's one in the win column for him.
Meanwhile, on the home front, Karl is living on shaky ground. His mom, widowed almost four years ago when his dad died of lung cancer, has gone over the edge and now spends most of her time getting drunk and high and having sex, spending Karl's wages from his five jobs, and investigating theories that link President Nixon to UFOs. She also is literally a crazy cat lady, with dozens of cats that roam the house and are regularly buried en masse in the backyard. Oh yeah, and Lightsburg is a small town and Karl's dad used to be the mayor, so everyone knows about his mom going off the deep end.
Sheesh. No wonder Karl wants to be normal.
Anyway, with his get-out-of-therapy letter safely in his locker, everything appears to be coming up Karl. There are a couple of glitches in his plan, though. The first is Marti Nielsen, the new girl in school and the newest member of the Madman Underground. Marti comes from a mega-dysfunctional family, but she is a really cool girl who is totally unapologetic about how weird she is, and she kind of gets Karl thinking about what it would mean to lose the therapy group members as his friends. He also seems to kind of like her—just a little.
The other problem is Paul, who isn't talking to him at all. He later tells Karl that he, too, is trying to be normal and get out of therapy, and he believes that interacting with Karl would ruin his plan. The two get in a humongous fight about this in the hallway, and there's serious tension between them for the majority of the book. The whole situation ultimately gets Karl thinking about whether he really wants to lose his best friend, let alone the rest of the Madmen.
A lot of things happen over the course of the week that reinforce this for Karl. For instance, after the football game on Friday night, the gang has to go to Toledo to rescue Paul—who had a fight with his dad and is cruising the section of town where gay people hang out—and keep him from getting beat up. As a result, Paul and Karl make up and spend most of the next night working out their conflicts.
By Sunday night, when a fight with his mom and a lockout at Marti's house forces the two to share a hotel room downtown, Karl has started to realize that the Madmen may be weirdos, but they're his weirdos—and his best friends. On Monday morning, after an extremely awkward encounter at the hotel with his and Marti's moms, Karl goes to Gratz's room, makes sure the magic letter goes in the trash, and heads to therapy with his comrades.
That's not all, though: A serendipitous meeting between Gratz, Karl's AA sponsor, and his mom's boyfriend results in Karl finally getting some help for his home situation in the form of a bank account so that he no longer has to hide his money all over the house and risk his mom stealing it. By the end of the book, Karl finally seems to have some peace about who he is, who his friends are, and whom he can count on.