One of the many films about murderous animals to come out in the wake of "Jaws", Robert Forster plays detective David Madison, a tough Chicago cop who's trying to solve a series of grisly murders that have been taking place down in the city sewers. Several workers have mysteriously vanished and parts of them have been turning up at one of the city's filtration plants.
But as he is soon to discover, this is not simply a case of a maniac on the loose. After heading on down into the sewers with another officer, he finds the thing responsible for the recent slew of killings is in fact a giant alligator. It turns out this thing was flushed down the toilet as a baby, but has grown to gigantic proportions after eating the bodies of some dead dogs dumped down there by a nearby research facility that were pumped full of growth hormones.
At first the police chiefs don't believe his story about a giant alligator in the sewer, but after discovering the remains of a nosey newspaper photographer and finding the final pictures he shot, they realise Detective Madison was indeed telling the truth. So the fun begins as the SWAT teams head into the sewers, but the Alligator decides to break out and head into town, munching on unwary passers by. Police start combing the lakes and rivers and even enlist the help of an alligator hunter named Colonel Brock (Henry Silver), who only ends up serving as more gator bait.
Written by John Sayles, who also scripted "The Howling", this features some excellent scenes, from the swimming pool scene at a kids fancy dress party, to the wedding party massacre and the bit where it upturns the river police boat. Not to mention the "big budget" special effects scenes of (what is obviously) a small alligator on a scaled down set.
Good fory, fun and packed full of action, this is "vintage" early 80's horror fare at it's finest.