When the rat population of Toronto is exposed to an illegal growth drug as a result of consuming contaminated grain, they begin to grow to enormous sizes and attack the city's residents. It's now up to high school teacher and basketball coach Paul Harris (played by Sam Groom) to stop them. Along the way there are various subplots such as Harris' attempts to woo the local health inspector (Sara Botsford) while dodging the advances of high school cheerleader Trudy (Lisa Langlois).
James Herbert himself was extremely dissatisfied with the manner in which the filmmakers adapted his story, calling the film "terrible, absolute rubbish".
This film contains examples of the following tropes:
- Badass Teacher: Harris, who single-handedly annihilates a large number of rats at the climax.
- Black Dude Dies First: Averted in that Foskins isn't actually the first to die but his death does foreshadow the arrival of much greater dangers.
- Bus Full of Innocents: Or in this case, a subway train, whose route takes it directly into the path of a hungry pack of rats.
- Death of a Child: The film's most infamous scene is the rats breaking into a home and eating a baby that is inside, leaving nothing but a gigantic splatter of blood and the poor child's gnawed clothing.
- Dropped a Bridge on Him: Trudy and Martha are both trampled to death by fleeing patrons during the rats' theatre assault.
- Hot for Teacher: Trudy's infatuation for Harris is one of the running sub-plots of the film, culminating with her breaking into his home and waiting for him in his bed in her underwear. Causes some expected Not What It Looks Like when he tells her to get out and his Love Interest happens to be waiting in the kitchen.
- Karmic Death: The mayor ends up sacrificing an entire group of people, leaving them to be eaten by the rats while he escape with the subway train. Turns out some of the rats already got in the train, and they have already killed him by the time it makes it to the station.
- Kill It with Fire: Harris manages to kill most of the mutated rodents by igniting some nearby drums of flammable liquids. However, some of them remain alive onboard the subway train and proceed to kill the mayor and feast on his corpse.
- Mayor Pain: The mayor of Toronto is portrayed in a manner similar to Mayor Larry Vaughn in Jaws, in that he seems more concerned with making sure the new subway section's inaugural run proceeds on schedule than with the giant rat infestation that threatens the city's populace.
- Mr. Fanservice: Harris appears shirtless in at least one scene.
- Ms. Fanservice: Trudy in her underwear.
- Rodents of Unusual Size: The rats are transformed into these after ingesting the steroid-laced grain.
- Shout-Out: During the theatre attack, the film being shown is the director's own Enter the Dragon.
- Screw the Money, I Have Rules!: The health inspector's Establishing Character Moment is her inspecting the steroid-laced food that is the cause for this whole mess and discovering that it's both tainted and has very obvious marks of having been eaten by rats for some time now and she orders its immediate destruction, a decision she maintains even when the food company's Corrupt Corporate Executive tries to buy her off and then goes over her and complains to her supervisor by alleging that she's overreacting.
- Swarm of Rats: Goes without saying. Turns out that food contaminated with steroids is the cause of this.
- Terrifying Pet Store Rat: For the film to have rats the size of small dogs on some scenes, they were literally played by small dogs; the filmmakers dressed some dachshunds with specially made ratsuits.
- Would Hurt a Child: One especially cruel scene has the oversized rodents killing a baby girl left unattended in her high chair before setting their sights on her sister.