Four years on from the horrible shark attacks which plagued Amity Isl&, Police Chief Brody (Roy Scheider) is still uneasy about the prospect of another shark visiting the bay. So when the film developed from the camera of a missing diver shows what looks like a shark fin, he begins to get very worried indeed. However, Mayor Larry Vaughn (Murray Hamilton) again plays down the incident, & when Brody raises a panicked false alarm from his observation tower on the beach, the mayor even goes as far as firing him. It is then that the bloodbath really begins.