The film shows how, in 2010, Foster began free-diving in a cold underwater kelp forest at a remote location in False Bay, near Cape Town, South Africa. The location was near Simon’s Town on the Cape Peninsula, which is exposed to the cold Benguela current of the Atlantic Ocean. He started to film his experiences and, in time, a curious young octopus captured his attention. By visiting her den and tracking her movements every day for months, he won the animal’s trust. In the film, Foster describes the impact on his life of his relationship with the octopus. The film shows the octopus defending herself against pyjama sharks. In one attack, the octopus loses an arm, and then retreats to her den to recover, regenerating the arm. Later, after mating with another octopus and producing a large number of eggs, the octopus dies and the film shows a shark taking her body away. Foster then describes the effect of his experience with the octopus on his relationship with his son, and his son’s development as a diver and student of marine life.