Decades ago, as a child, I read a book about a guy who befriends an octopus, becoming aware of its intelligence and curiosity and then having to live through the drama of his friend dying. My Octopus Teacher is basically the same thing, only it's a documentary. Octopi are marvelous creatures, both in their weird biology and their incredible intelligence. Numerous anecdotes have them use tools, enjoy beauty and create artistic work, be able to personally connect to the people they encounter. That is amazing from a completely non social creature that can rarely live more than a year. In terms of intelligence, no animal or man comes close in that small time span.
But these are just facts. The documentary is a personal account from a guy who by chance became fascinated with such a creature and spent a year diving underwater without a wetsuit or an oxygen tank and studying it, earning its trust and caring about it. You can see, in his narration, how difficult it was to just keep the distance necessary to observe the life of the octopus and not become part of it. There are scenes when the creature jumps on his hand and then explores his chest, cradling to it and accepting warmth and petting. It is that personal approach to the documentary which makes is so powerful.
Bottom line: this is the story of the life of one specimen of Octopus Vulgaris, as narrated and video documented by the film maker. The images are very beautiful and the account personal and lacking the fillers or pointless flourishings of common documentaries. The viewer is drawn into the life of this amazing creature. It's a good film.