The Monster Squad is a society of young teenagers who idolize classic monsters and monster movies. In addition to a clubhouse in a tree, they actually have their own business cards. Club leader Sean (Andre Gower), whose five-year-old sister Phoebe (Ashley Bank) desperately wants to join the club, is given the diary of legendary vampire hunter Abraham Van Helsing (Jack Gwillim) – but his excitement is somewhat toned down when he finds it’s written in German. Sean, his best friend Patrick (Robby Kiger), and the rest of the Monster Squad get their local “Scary German Guy” (Leonardo Cimino) to translate the diary. (When he is asked how he knows so much, he tells them cryptically that he has “some experience with monsters.” When the children leave his home and he closes the front door, a concentration-camp number tattoo is revealed on his forearm.)

The diary describes, in great detail, an amulet that is composed of concentrated good. One day out of every century, as the forces of good and evil reach a balance, the otherwise-indestructible amulet becomes vulnerable to destruction. The next day of balance falls within a couple days, at the stroke of midnight.

The kids realize they must gain possession of the amulet before the day of balance arrives; once they have the amulet, the kids can use it — with an incantation from Van Helsing’s diary — to open a hole in the universe and cast the monsters into Limbo. As shown in the prelude, van Helsing had unsuccessfully attempted this one hundred years ago in order to defeat his old adversary Count Dracula; he subsequently hid the amulet in America, where it was out of Dracula’s immediate reach. Dracula, meanwhile, must obtain the amulet before the Monster Squad does, so that the Count can take control of the world. To this end he assembles several monstrous allies: Frankenstein’s monster, a werewolf (a reluctant ally in his human form), a mummy, and an amphibious gill-man, in addition to three teenage girls whom the Count transforms into his vampiric consorts.

The amulet turns out to be buried in a stone room, under a house that Dracula and the other monsters now occupy. The aforementioned room is littered with holy symbols, including crucifixes, which prevents the monsters from simply taking it. Luckily, the Monster Squad has the assistance of Patrick’s lovely-but-nameless elder sister (Lisa Fuller), because the incantation must be read by a virgin, and she’s the only person they know who speaks German. Sadly she is failing German and technically not a virgin (“Well, Steve… but he doesn’t count.”) Additional help comes from Sean’s father, a local police detective who was at first highly sceptical of Sean’s hobby and the seriousness of the case, and Frankenstein, who defects after befriending Phoebe, who ultimately is the virgin needed to read the incantation with the assistance of “Scary German Guy”.