The prismatic hologram cover design consists of light-blue swirls, and the cover illustration consists of a boy trapped inside of a sandwich of Purple Peanut Butter.
You have flown to Fiskeville to spend the summer with your aunt and uncle and their two children, your cousins Drippy Dora and Barney the Brute. Barney tells you to play hide-and-seek; whoever is found, Barney gets to pound. You hide in the basement, something your Aunt tells you not to do, because the people who lived there before them were strange and they never got around to cleaning it out. You get hungry and spot an old refrigerator. There are only two things inside: A jar of purple goop, and some stale chocolate cake. If you eat the purple goop, which smells like peanut butter, you wind up shrinking; here, you face the possibility of becoming one of Dora's toys, being locked in the refrigerator, being flushed down the toilet, or fighting a now giant mouse. If you choose the cake, you wind up growing into a giant, and facing the possibilities of being chased by the local police who think you are a giant, being pounded by Barney, or intimidating Barney and Dora.
There are twenty one bad endings and six good endings.
- While in the sewer, a Monster Blood can floats by and you decide to open it. However, it's empty, and fills with sewer water until it sinks. You end up drowning in the sewer.
- Puff grabs you in her mouth while she plays with you. When she opens her mouth again, you are dropped on the ground, and get killed by the fall.
- Stuck inside the refrigerator until you die.
- It is implied that you were destroyed by the mouse.
- Effy gives you two beakers of liquid. When you pick the purple liquid, you find out it was the wrong one because you've become a gingerbread cookie.
- Straining under the weight of Dodo the elephant, everyone in the circus realizes you're nothing but a fraud. You are chased out of the three rings, and you get a job cleaning up after Dodo at the circus.
- The mouse decides to adopt you and places you alongside its children.
- Grabbing Barney, you try to get even with him. But then you shrink down to your normal size, and Barney finds out it was just you all along. It's likely that Barney's going to beat you up.
- Shrink down to your normal size with five tigers in your lap.
- The government thinks you're an alien and captures you with an artificial spiderweb net.
- When your coin comes up the same way three times, you guide the Popsicle stick (as a boat) over a waterfall. But then you realize the waterfall was the main pipe to the sewage treatment plant. You're about to float into a grinder.
- The dolls in the dollhouse reveal that they can talk and move. You become the new housekeeper for a doll family in Dora's dollhouse.
- After trying the Super-Duper-Reducer machine, you are back to your normal height. But your arms are too long, your legs are too thick, and your head is too small.
- You test out the steaming room, because people have lost weight with it. But inside it, you fall asleep for too long and shrink down to a raisin.
- Heading for a pile of twisted metal, it is implied that you will be crushed in a car as it enters a car crusher.
- Several science books fall off of the shelves, squashing you.
- Awakening in what you think is your bed, you suddenly realize you're now a resident of Dora's dollhouse.
- After eating all of the mixture the mystic gave you, you grow so big your head reaches outer space, and you end up unable to breathe.
- About to shrink down to nothing when looking for Aunt Fiona.
- Crushed to death when the janitor faints.
- You are back to your normal size, but you've become magnetized. Wanting to see what other abilities you possess now, you try it out at a recycling center. You're about to be crushed by hundreds of recyclable cans.
- Shrink down to your normal size, and avoid being captured by the government.
- Grow back to your normal size, and have an elephant-sized lizard to protect you from Barney and Dora.
- Effy turns you back to your normal size with the help of chocolate cake dipped in blue liquid.
- Grow back to your normal size, but become stronger and quicker to defend yourself from Barney and Dora.
- Switch bodies with Dr. Abbott, who gets to spend the summer with your cousins.
- You're back to your normal size, but you're magnetized now. You pass by a pay phone, and seventy-three dollars in change gets stuck all over you.
Cover Art Gallery
- This book is probably a homage to the Monster Blood books.
- The purple peanut butter seems to be the opposite of Monster Blood (it makes people shrink, not grow).
- One of the youngest Monster Blood characters (Evan Ross' cousin Kermit) is referred to as an adult in this book.
- Considering this and the previous fact, It's most likely that the the third solution in the ending of Monster Blood III might be connected to or implied to be the Purple Peanut Butter.
- You're actually your normal height when you get stuck in the refrigerator despite eating the purple peanut butter.
- The change ending would not actually occur in real life, as coins are not attracted to magnets.
- Purple Peanut Butter appears as an item in Goosebumps: The Game.