Sleazy pet store owner Lou Gutchel (Sydney Lassick) has been dog-snatching puppies for the illegal research experiments of unscrupulous pharmaceutical executive Slade (Dean Jagger).
Meanwhile, a pet baby alligator flushed into the Chicago sewer system has grown to an enormous size by feeding on the illegally dumped carcasses of pets from Slade Laboratories which is conducting experiments on how to genetically increase the size of animals.
Detective David Madison (Robert Forster) meets herpetologist Marisa Kendall (Robin Riker) while investigating both the pet disappearances and a spate of dismemberment murders in the sewers.
Nobody believes him after he barely escapes from a massive, 36-foot killer gator loose in the streets beneath Chicago. This creature is gigantic, voracious and insatiable – and it will eat anything (as you might imagine, considering where it lives).
But a suspicious reporter (Bart Braverman) decides to take a look for himself and comes up with something completely new in pictorial journalism – he achieves the impossible by photographing himself being eaten alive!
The authorities have to take notice of the reporter’s photographs and hire a grizzled hunter, Colonel Brock (Henry Silva), to wipe out the monster. While Madison and Kendall investigate Slade Laboratories, the State troopers and the National Guard embark on a plan to flush the giant alligator out into the open.
The operation proves more successful than they bargained for and when the monstrous reptile breaks cover, all hell is let loose in the city. After going on a rampage through the city streets, the alligator pauses only to chew up the corrupt Mayor (Jack Carter) and beat the villainous Head of Slade Laboratories to death with his tail, before heading back to the sewers hotly pursued by Madison and Kendall.
At the outset, the film smacks of just another absurd horror outing, but director Lewis Teague quickly lays on the style and excitement.
There are polished special effects, a serviceable script and capable performances from Forster and Riker. This reptile is not a match for the shark in Jaws, but it does have plenty of bite (sorry!). An almost completely unrelated sequel, Alligator II: The Mutation, was released in 1991 to universal scorn.
Detective David Madison
Police Chief Clark
Michael V. Gazzo
John Lisbon Wood
Royce D. Applegate
Charles R. Penland