The alligator begins ambushing and devouring sewer workers it encounters in the sewer, and the resulting flow of body parts draws in world-weary police officer David Madison (Robert Forster) who, after a horribly botched case in St. Louis, has gained a reputation for being lethally unlucky for his assigned partners. As David works on this new case, his boss Chief Clark (Michael Gazzo) introduces him to reptiles expert Marisa Kendall (Robin Riker), the woman who, as a teenager, bought the alligator years earlier, unaware that this alligator is her former pet. The two of them edge into a prickly romantic relationship, and during a visit to Marisa's house, David bonds with her motor-mouthed mother.