Ramon, a 32-foot-long alligator who was born as a baby and flushed into the city sewer, is now a menacing creature that devours both animals and people. His massive size comes from his diet of dead pets, which are treated with growth hormones, allowing him to grow for 12 years. Now, Ramon is angry and looking for revenge, and only detective David Madison knows about his existence. He is tasked by Sayles' script to prove to the rest of the city that a tropical beast lives in their midst, creating an entertaining romp through the sewers of Chicago.