The story starts with Mike, a carpenter who's been out of work for a while. He wants to give his son, Cam, a cool birthday present, but all he can afford is a 78-cent cardboard box from a mysterious old man with a lazy eye named Gideon. Mike and Cam make the most of the lame birthday present by cutting and pasting the box into the shape of a cardboard boxer – who magically comes to life. The worst present in the history of birthdays quickly becomes the coolest birthday present in the history of the universe.
When their nuisance of a neighbor Marcus finds out about the cardboard boxer, he steals some of the magic cardboard to make his own monsters. It's a foregone conclusion that his creations turn on him. With cardboard creatures rampaging all over the neighborhood, Mike, Cam, and Bill the cardboard boxer must step in to save the day.
This book provides examples of:
- Attack of the 50-Foot Whatever: The giant Cardboard Marcus in the cardboard monsters' world.
- Become a Real Boy: Bill the Boxer wants to be human. It's implied that he got his wish in the end.
- Bigger on the Inside: The cardboard monsters somehow manage to build an entire world inside Marcus's house.
- Brick Joke: Early in the book, Mike snarks that Marcus should get a haircut. At the end, after losing his house to cardboard monsters, we see Marcus got that haircut after all.
- Cool Shades: Pink Eye has these to hide his, well, pink eyes.
- Creator Thumbprint: No cats, and not many blatantly Christian elements (although you will find some Christian messages if you look closely), but we've got monsters galore, a speechless final page and plenty of "reverse silhouette" panels.
- Deadpan Snarker: Mike has his moments.Marcus: Hey, planet killer! Get a hybrid!
Mike: Right after you get a haircut!
- Eldritch Location: The cardboard monsters dig up Marcus' house and create their own world underground.
- Heroic Sacrifice: Bill uses the cloud bomb to destroy the cardboard monsters at the end, knowing it will kill him too.
- Kill It with Water: The cardboard creatures are susceptible to water.
- Maybe Ever After: Mike with his neighbor Tina by the end.
- Missing Mom: Cam's mom and Mike's wife, Carol, died before the story begins.
- Ninja Pirate Zombie Robot: The pilot of the UFO that made the magic cardboard was an alien wizard who had an inhuman grasp of quantum particle science. And was also religious.
- Nosy Neighbor: Marcus.
- Rule of Cool: The boxing match between Bill and the Death Boxer doesn't have much to do with the plot, but it's cool.
- Running Gag: Mike sure gets punched in the jaw a lot.
- Screw the Money, I Have Rules!: After Mike explains how he doesn't even have money for a birthday dinner for Cam, his boss, Mr. Machousky, tries to give Mike some money from his own wallet to help out, but Mike turns the offer down for this trope.Mr. Machousky: Well, you're in luck! I've got a heart and you're breakin' it right now! Don't tell anyone...but I think I can float you a little something 'til things turn around for you. I know you're good for it.
Mike: Thanks, boss, but I came in for a job, not a handout.
- Screw This, I'm Outta Here: Marcus's henchman Pink Eye quotes this before bolting for the door.
- Sorcerer's Apprentice Plot: Marcus steals Cam's cardbord maker and uses it to make a whole army of cardboard monsters, crowning himself king over them. However, the monsters quickly get tired of working for Marcus and make a cardboard copy of him, making the cardboard Marcus king.
- Wizards from Outer Space: According to Old Man Gideon, the magic cardboard aparently came from the parts of an alien ship that merged into the walls of the cardboard shipping boxes. Said alien ship was piloted by a alien wizard who was a particle physicist experimenting on subatomic space travel. It's ambiguous if this is actually true or if Gideon was just making it up.
- What the Hell, Hero?: Cam calls Mike out for trying to leave Bill to fend for himself.