All poor Al wants for his birthday is a pair of roller blades. Unfortunately, he belongs to a family of brains who seem more concerned with teaching their pets stupid tricks than paying attention to him. Seriously, his sister Michelle taught her cat Chester to count, pull down the blinds, and use the electric can opener when he wants food. They also keep forcing him to study for the upcoming Science Bowl and reminding him that Michelle won every year she was in middle school.
The day of his birthday arrives, and his family seems pretty excited about his gift. Instead of new blades, he gets a chemistry set. To add to the fun, his parents decide that he can't actually use it until Michelle goes over all the safety regulations with him, and she's far too busy with her science club to help him in any way. He resigns himself to spending time with his dog Tubby, who is the stupidest dog in the world, and moping over his present.
When his best friend Colin discovers his present, he starts mixing things together to create a stink bomb. Al stops him because he's worried about an explosion, and Colin finds an orange slip of paper with instructions on how to make a stink bomb in the kit. Al thinks it's a little weird that it's on different paper than the rest of the instructions, but they do it anyway. They sneak it into the living room, where Michelle's club meets, but nothing happens.
When they head back into the basement, they find that the orange stuff in the beaker is suddenly a blob. Colin accidentally pours it onto the table and it starts going everywhere. After touching it with his bare hands, Al uses paper towels to grab the ooze and move it into a trunk. He does notice that it keeps breaking off into tiny balls before rolling back together. Chester also gets the ooze on his paws and he suddenly becomes stupid. The cat can't remember any tricks and barely remembers to use the litter box.
The next day, Al feels a little different. He puts his shoes on the wrong feet, can't remember basic things, and just plain feels groggy. He gets in trouble at school for not paying attention, and the school bully, Eric, goes off on him for giving him a wrong answer. His haze gets even worse the next day, and Eric makes him do his homework, but he can't remember how to add or multiply. Eric decides to beat him up and follows him after school. He manages to get away by hiding on Fear Street, but then he realizes that he's lost. Colin finds him and it turns out that he's only a few blocks from his house.
Al knows that something happened with the ooze but no one wants to listen. Michelle wins some big prize, and his parents decide that he's just acting out, so they make him stay home while they go out to celebrate. He puts some of the ooze in a container to take to his science teacher for help. During a meeting of the Science Bowl, the other members see it and start playing with it, and they get pissed because he flips out.
On the day of the Science Bowl, no one can remember even the most basic of questions. Al gets the only correct answer, which is one that his family tested him on that morning. Everyone gets in trouble, and the school cancels the event because they think the kids were all just goofing around. He and Colin finally decide that they need to confront the ooze.
The ooze is now one huge mass that rises up from the trunk and becomes a 12-foot tall blob. It reveals that it comes from an alien race that needs smart brains to survive. They slipped themselves into science kits because they assumed that the kids would go to smart kids. It takes Chester's brain and attacks Tubby, taking his brain too.
The blob comes after Al and actually manages to get his head in its mouth before it starts convulsing and seemingly dies. Al watches as its brain goes from really big to teeny, tiny, and he realizes that it's because it tried to take Tubby's brain and the dog is so stupid that it killed the blog. The two boys celebrate by stuffing it back into the trunk, dragging the trunk outside, and burying it in his backyard.
A few days later, he and his family are outside spending time together. Michelle notices some weird orange blobs in the yard, and he tells her not to touch them because they might be toxic. His parents agree but she grabs a handful anyway, and Al points out that his sister was always too smart for her own good.
*His parents are insane! They let Michelle create a literal bomb that explodes when he walks down the stairs to introduce him to the chemistry set, yet they won't let him play with it.
*While in his "stupid" state, Al actually walks face first into a glass door because he can't remember how to open it.
*Al says that Tubby no longer has a brain because the ooze took it, but Chester is suddenly fine, remembers all of his tricks, and is learning some new ones. The ooze ate both their brains, so why is Tubby the only one who got screwed?
*You know what's awesome? When you give a kid a birthday gift and then tell him he can't touch it for days/weeks. Oh, and when he does touch it, you yell at him for potentially messing things up. Nice.
*Ghosts of Fear Street make me a little sad. There's only one mention of Fear Street, and Al mentions in passing that his sister goes to Shadyside High School. Stine could have set this series anywhere.