A scuba diving instructor, her biochemist boyfriend, and her police chief ex-husband try to link a series of bizarre deaths to a mutant strain of piranha fish whose lair is a sunken freighter ship off a Caribbean island resort.

Megan Carter is a reporter duped into running an untrue story on Michael Gallagher, a suspected racketeer. He has an alibi for the time his supposed crime was committed but it involves an innocent party. When she tells Carter the truth and the newspaper runs it, tragedy follows, forcing Carter to face up to the responsibilities of her job when she is confronted by Gallagher.