A group of preteen friends, united by their love for classic monster movies, form a club known as "The Monster Squad." Their passion for creatures of the night is put to the test when they stumble upon an ancient diary belonging to the legendary vampire hunter, Abraham Van Helsing. The diary contains the secret to vanquishing evil for good, but the text is written in German, which leaves the Squad at a loss. As fate would have it, the small town they call home becomes the nexus of supernatural occurrences when a powerful amulet with the potential to open a portal to a dimension of evil surfaces after 100 years.

Supernatural forces align as Count Dracula, seeking the amulet to unleash darkness upon the world, assembles a frightening ensemble of iconic monsters: the Mummy, the Wolfman, the Gill-Man, and Frankenstein's Monster. Unbeknownst to the adults, who are dismissive of the children's concerns, the Squad must face their fears and confront the monsters invading their town. With the aid of the diary, the kids enlist the help of the "Scary German Guy," a local recluse, to translate Van Helsing's work and uncover the secret to stopping Dracula's diabolical plan. As the night of an impending eclipse draws near, a race against time begins for the Monster Squad to find the amulet, decipher the diary's contents, and set up a showdown with the forces of darkness.