Known for their boundless grace and playful energy, captive dolphins are always eager to please and perform. However, at home in the open sea there's another little-known side to these awe-inspiring mammals that's powerful, cunning and ruthless. Witness a team of dolphins coordinate a devastating attack on a massive school of fish. See the largest, most fearsome member of the dolphin family, the killer whale, capture its next victim and observe as young dolphins learn how to hydroplane through inches of water to catch fish. This programme explores the secret side of these sociable yet aggressive creatures.