Successful forensic psychologist Alex Cross discovers that his niece has gone missing. Once he consults with police Detective Nick Ruskin, Cross believes that the disappearance is the work of an insane killer known as ''Casanova.'' Meanwhile, Dr. Kate McTiernan is kidnapped by this criminal and witnesses many other imprisoned women in his lair. After narrowly escaping, McTiernan teams up with Cross to try to apprehend the deranged Casanova.