Underwater cameraman Bob Cranston captures mesmerizing footage of one of the most ancient animal classifications on earth: Cephalopods, marine mollusks related to snails and clams. Their complex behaviors, astonishing body adaptations and, especially, their compelling eyes, could be from an alien science fiction world. They are the most intelligent invertebrates, but they are also deadly predators and combatants. These "sea monsters" reflect the amazing diversity of life on our planet.