Naturalist Steve Backshall heads underwater to fulfil his wish of studying four monstrous animals to find out more about their behaviour and communication techniques. Scientists and extreme divers study the fascinating but deadly animals, then locate the creatures to allow Steve to do the unthinkable: swim with the monsters. Among the animals that Backshall tries to accompany are the hippopotamus, the anaconda, the illusive giant Humboldt squid, and one of the world's most-feared creatures: the great white shark.