Victor Frankenstein is a boy who lives with his parents, Edward and Susan Frankenstein and his dog, Sparky, in the quiet town of New Holland. New Holland is a beautiful town, but its mayor, Mr Burgemeister, is very serious and grumpy.
Victor loves making films with his dog and perfom science experiments in his attic. Victor's intelligence is recognized by his classmates at school, his somber next-door neighbour, Elsa Van Helsing, mischievous Edgar "E" Gore, obese and gullible Bob, overconfident Toshiaki, creepy Nassor and an eccentric girl nicknamed Weird Girl. Victor's father encourages him to play baseball and leave the attic lab. Victor hits a home run at his first game, but Sparky, pursuing the ball, is killed by a car.
Victor is now very depressed. Inspired by his science teacher Mr. Rzykruski's demonstration of the effect of electricity on dead frogs, Victor digs up Sparky's body, brings him to his laboratory in the attic, and reanimates him with lightning. Seeing Weird Girl's living cat, Mr. Whiskers, the undead Sparky escapes from the attic and explores the neighborhood. He is recognized by Edgar, who forces Victor into teaching him how to resurrect the dead. The two reanimate a dead goldfish, which turns invisible because there is an error with the experiment.
When Victor’s classmates discover Victor's reanimation formula they separately perform their experiments, which go wrong and turn dead animals into monsters: Mr. Whiskers holds a dead bat while it is electrocuted, turning him into a vampire cat; Edgar turns a dead rat he found in the garbage into a wererat; Nassor revives his mummified hamster Colossus; Toshiaki's turtle Shelley is covered in a growth formula and turns into a giant monster; and Bob's Sea Monkeys grow into amphibious humanoid monsters. The monsters escape into the town fair where they will unleash a tragedy.