Evan now lives in Atlanta where he gets ridiculed all of the time by a bully named Conan. Mr. Murphy, his teacher, apparently doesn't give a shit because he totally lets the guy run loose over his classroom. When Conan tells Evan that he can punch him once, he hits him in the stomach, and the teacher sees. He blames Evan and punishes him by making him take care of the class hamster Cuddles every day.
Luckily, his friend Andy just moved to Atlanta to live with her grandparents while her parents spend a year working in Germany. She brought a can of monster blood with her, but Evan begs her to get rid of it. Conan sees them and tries to take the can, but Evan drops it and pretends like he never had it. After he leaves, they bury it under a tree in the woods.
Conan continues being a huge jerk. Evan tries out for the basketball team, and Conan throws the ball twice in his face and he and his friends trip him constantly. After Conan stuffs him in the hoop, the teacher (who is also the coach) tells Evan that he's just too short for the team. Andy suggests feeding Conan some of the monster blood, and they sneak back into the woods to discover that he found the canister and stole it.
They decide to sneak into his house and get back the monster blood. They manage to find the can in his bedroom, but he and his parents come home. They basically climb out on the window ledge and drop to the ground to get away, and even then he almost catches them because Evan dog follows and starts barking. The monster blood started growing in the canister so they agree to bury it again.
Andy suggests feeding Cuddles some of the monster blood, but Evan disagrees. When he gets to school the next day, Mr. Murphy lectures him on overfeeding the animal, which suddenly looks a little bigger. By the next day, the hamster is the size of a small dog, and Evan leaves him tied up to the teacher's desk. The teacher is surprisingly happy, thinking that the hamster will make him famous.
Andy admits that she fed him a little monster blood, but only because she wanted to make Evan laugh. Cuddles keeps growing until he's nearly ten feet tall. Luckily, Evan's dad was working on a new sculpture that looks like a giant hamster wheel, and he entered it into a contest at the school. They find it and drag him back to the science lab, but Cuddles just picks it up and tears it apart.
Evan goes with Andy to her locker where she stored the monster blood. It's now taken over her locker, but he still manages to eat it and grow as tall as the hamster. He starts fighting with Cuddles and it looks like the hamster might eat him, but then they both shrink to their normal size. Andy discovers that the expiration date on the monster blood was that day, so the magic disappeared.
Mr. Murphy feels bad for how he treated Evan, so he comes by his house and presents him with Cuddles as a gift. Andy comes over and drags him away, saying that she has a surprise. It turns out that her parents sent her a new can of monster blood from a toy store in Germany. She leaves it on his desk, and when the book ends, they discover that Cuddles escaped from his cage and is eating the new monster blood.
*I know I said this earlier, but Conan is a real dick! He literally squeezes Evan's hand until it looks like raw hamburger, and he does it multiple times!
*Mr. Murphy is clearly the worst teacher in the world. He believes everything Conan says, including the time where he says that Evan threw the hamster out of the window and a car almost ran it over...on the playground.
*I also find it hard to believe that Evan is the only person who had a problem with Conan at that school.
*Evan is kind of a dumbass though. He tells everyone at his new school, including his teachers, about the monster blood and how it works, and then he doesn't understand why they all think he's a moron.