David Attenborough narrates a look at monkey intelligence, arguing that primate behavior holds up a mirror to our own. Capuchin monkeys in South America crack nuts with stone tools, and Japanese macaques wash food and pass the habit on to their young, evidence that these skills are learned rather than instinctive. The film moves through memory tests, problem-solving experiments, and footage of wild troops navigating rivalries, alliances, and deception within their groups. Baboons and vervet monkeys demonstrate social maneuvering that looks less like animal instinct and more like calculated strategy, tracking who owes whom a favor and who cannot be trusted. Attenborough's narration keeps returning to the same question underneath the footage: how much of what we call uniquely human intelligence actually predates humans by millions of years. The photography ranges from rainforest canopies to open savanna, catching behavior that took researchers years of patient observation to document.