For primates, family matters. They have the most complex social lives of any animal group on the planet. From dusky leaf monkeys who compete to babysit an infant to gibbons who learn dare-devil treetop acrobatics with their playmates, friends and family are at the heart of primate life. In the Amazon we meet a female spider monkey elder, who leads her troop to a unique food resource: aquatic plants brought within reach on raging floodwaters. She shows them how, using their remarkable tails as a safety rope, they can feast on this unlikely bounty. In Sri Lanka, we meet the bizarre slender loris in the most intimate images ever captured of the species. And in Brazil's Atlantic forests, we share a day in the life of the most devoted primate dad of all. The diminutive male golden-headed lion tamarin is a guardian, a navigator and, when needs must, a taxi service for his demanding offspring. With family comes hierarchy, and those at the top are constantly under threat. For a battle-scarred hanuman langur, attack is the best form of defence when his troop are threatened by a band of bachelors. In Morocco, an old male barbary macaque must find new friends to huddle with when freezing temperatures and a sudden snowstorm threaten his survival. This is our own animal family, but one about which we still have so much to learn. In 2017, news broke of a new species of primate, the Tapanuli orang-utan, and we share some of the very first moving images of mother and infant. Already, they are some of the most threatened great apes on the planet. This is the definitive portrait of our closest relatives, at a crucial time. Fascinating social behaviour, new species and unforgettable characters. Meet primates at their most social.