Evan still has a completely rational fear of Monster Blood given what happened in the last books. He hates the stuff so much that he can't even eat green Jell-O anymore. He also has a new job: baby-sitting for his cousin Kermit. His mom points out that his aunt can't afford to hire anyone else. Given that she only pays him $3 an hour, I can understand why no one else will do it.
It also turns out that Kermit is the type of kid I would totally punch in the face. Conan, his next door neighbor, goes to school with Evan and picks a fight with him. Kermit shows up, threatens to cover him with an invisibility potion he made, and then throws it on him anyway. All it does it make his favorite shirt disappear, which leads Conan to punch Evan in the face.
At school the next day, Andy teases him because she got a canister of Monster Blood from her parents and says she put it in his sandwich. He then makes her go to his cousin's house with him. Kermit asks Andy if he can do her math homework, makes a new potion that shrinks a mosquito bite Evan has, and then makes up something to cure his dog of hiccups. Evan forbids him from giving it to the dog, but he does anyway. The dog goes absolutely bonkers, rips up the basement, and acts nuts. Evan's Aunt shows up, Kermit cries, and he tells his mom that Evan teased the dog and made it go crazy. She screams at her nephew, coddles her kid like he's a baby, and threatens to fire Evan.
Cut to the next time he sits. He and Andy, who is pissed off because Kermit deliberately answered all her homework questions wrong, force him to go outside and play. He first makes them all a glass of orange soda. Turns out that he dosed it with something that makes Evan and Andy laugh uncontrollably. Conan then shows up when they accidentally toss a Frisbee in his yard. He freaks out when Kermit says they are laughing at Conan and threatens to kill them.
Evan and Andy decide to get back at him with some Monster Blood. They sneak some into his latest batch of whatever the hell he makes. Only this mixture explodes all over the place. Evan accidentally eats some, which makes him grow twice as big as them and then even bigger. They manage to get him out of the basement by pushing and pulling him up the stairs.
Once outside, he sees Conan picking on some little girl and threatening her with a baseball bat. He steals the bat and yells at Conan, who realizes that he ate Monster Blood. Conan keeps picking on him until Evan almost steps on him, and he then runs away. Kermit also makes him think he stepped on and squashed Andy before laughing at his own stupid joke.
Things go okay at first. He helps some kids get their kite out of a tree and plays baseball with some of his friends. Then Conan shows up with the cops and says that Evan almost killed him. Others show up and say he did all this destruction around town. The firefighters come out, turn on their hoses, and try to knock him down with water.
Evan manages to get away and find a place to hide. Kermit and Andy finally find him, and he comes up with a plan to coat himself in the shrinking liquid Kermit made before. They run back to Kermit's house, but he uses the wrong potion and turns Even bright blue. A second potion gives him feathers. The cops show up just as he finds the right potion and becomes his normal size. He falls asleep that night feeling great about himself, only to wake in the middle of the night and discover he's the size of a mouse. Just then, his dog rushes in, scoops him up, and carries him off as his dad wonders what the dog has in its mouth.
*Kermit tells his mom that the other kids drank all their soda and lost his Frisbee, so she demands Even buy him a new one. The lady seriously needs to focus on her psychopath son.
*I cannot possibly explain how much I hate Kermit. He is the ultimate whiner and a just plain bad character. Maybe Evan's aunt should take a look at how many sitters quit over the years and realize her little angel is really a demon kid.