The cover illustration shows the Blue Monster Blood multiplying in the bathroom.
Evan Ross' parents are going out of town for a week to Tucson, Arizona. While they are away, Evan is forced to stay at his annoying cousin Kermit's house. Kermit begins terrorizing Evan by placing tarantulas on his head. Kermit's mother also puts hot sauce on everything she cooks, including spaghetti that is so hot that Evan's lips swell up like "twin salamis."
Evan accidentally steps on Conan, the school bully's, brand new sneakers, and Conan stomps his sneakers on Evan's feet. Conan also pulls on one of Evan's sweater-sleeves.
Andy comes over to visit Evan and the three children have a Super-Soaker fight. This is a lot of fun, until Kermit sprays Conan's sneakers with water. Conan crosses the yard and sees that Andy has a can of Monster Blood. He forces her to give it to him and he opens the can and paper snakes come out.
Kermit brings his collection of mice out into the yard and sets them free. Evan can't understand why Kermit thinks the mice will not escape, especially since they are escaping. Kermit tells Evan he has installed a wireless electric fence along the perimeter of the yard. Then he realizes that he forgot to turn it on. Evan walks to the edge of the yard and Kermit turns the electric fence on, causing Evan to spastically dance from the shock.
Conan comes over to see what the hubbub is all about and he too gets shocked. He beats up Evan. Kermit is sympathetic to Evan's plight and presents him with the perfect revenge: he has developed a hair-growing formula. Kermit tells Evan that they could put some on Conan's hands, giving him "werewolf hands." Evan thinks giving Conan this is a great idea.
Andy shows up at Evan's window in the middle of the night. Andy shows him another can of Monster Blood that she found in the dumpster behind a science lab. She wants Evan to get revenge on Conan, by using the new Monster Blood. Kermit shows and opens the new can of Monster Blood. Conan also comes out into his yard and tries to take the Monster Blood, only to be shocked again by the fence. Conan retreats into his house and Andy tries to put the lid back on the Monster Blood, which is blue instead of the usual green.
The liquid Monster Blood has morphed into a small blue creature with black eyes and a big-lipped mouth filled with sharp teeth. Andy thinks the gelatinous creature is cute, until it hops across the yard and latches onto the water spout. The creature swells up like a balloon with water, until it explodes. The explosion sends a wave of blue slime over the children. Where there was one creature, there is now two. The creatures continue splitting, with each subsequent pair becoming meaner than the creature that spawned it.
The creatures start attacking the children, trying to suck the water from their bodies. One latches onto Andy's face and another on Evan's shoulder. The children try to force the dozen or so creatures into a plastic garbage sack. Kermit takes the sack into the house to hide it, as Kermit's mother comes out to blame Evan for all the damage the creatures have wrought on her yard.
The next morning, Evan asks Kermit where he hid the sack of creatures. Kermit hid the sack of creatures in the spare bathroom. Evan freaks out because the bathroom has four water fixtures and as the two boys make their way towards the bathroom, they can already hear the havoc being wreaked within. That spare bathroom is also where Kermit was hiding his hair growth formula. When the door is finally opened, the two are greeted with the sight of dozens of angry hairy creatures. Slime covers the walls and every few seconds there is another sickening *pop* and wave of slime as new creatures are formed.
Evan decides to round up the creatures and then lead them out into the yard to zap them on the invisible electric fence. Evan is shocked to discover that Kermit forgot to turn the fence on. The horrible little creatures escape into the neighborhood. The first place they head is Conan's house, where Conan has just stepped out into the yard again. The creatures swallow his can of Coke and start multiplying and exploding slime all over him.
Andy shows up and she and Evan track the moving wave of monsters down the street, as they head towards a public park. Along the way the monsters almost kill Kermit's dog and finally engulf Andy and Evan, until they all swarm off and huddle into one big pulsating ball. The monsters are so vile and evil that they have started to attack each other. One by one, they eat each other, until there are no creatures left. The children return to Kermit's house.
A scientist wearing a space suit shows up. He introduces himself as Professor Eric Crane from the Science Institute. He explains that this batch of Monster Blood was the result of ten years and $50 million of investment in the development of an underwater fighting force. He apologizes for being so careless. As he leaves, he asks Evan, Andy & Kermit not tell anyone about this. Evan says that he won't.
Conan comes out into the yard and tells the children that he found that blue candy they were hoarding. He tells them that he can't stop drinking water...and then three other Conans comes out of his house. The four Conans surround the children and the first one tells the children he feels MEANER than usual.
Monster Blood IV is one of the few books in the original series to not receive a television adaptation for the Goosebumps TV series.
Cover art gallery
- This is the last appearance of Andy, Kermit, Conan, and Trigger to date.
- There is none of the original Monster Blood in this book. There is only an entirely different type of slime, a scientific military defense experiment. The "blood" seems to resemble slugs or snails more than the actual monster blood. They are small, blue, liquid, have eyestalks, and mouths with sharp teeth. The only Monster Blood in the book is in Evan's Dream when Kermit's mice ate some of the "Green 'n' Real" Monster Blood.
- This is the second sequel to feature a different antagonist than the original antagonist, the first one being Night of the Living Dummy II.
- There are supposed to be 11 blue monsters featured on the cover of this book, but one monster in the medicine cabinet is obscured by the text bubble that says Watch GOOSEBUMPS On Fox Kids Network. The monster in the cabinet is visible on the Spanish cover. On the Russian cover, the monster in the cabinet was painted over.