Plot: In 1997, tourists on a whale-watching boat 27 miles west of San Francisco were stunned to see a great white shark being attacked, killed and eaten by an orca, effectively deposing the former as the marine world's most feared predator. Using footage from the incident, experts provide their theories as to how the killer whale was able to overpower its adversary, and question whether this event warrants a reconsideration of the ocean's food chain