On Thailand's East coast, Dr Amanda Tan reveals something rare in the animal kingdom: tool use. A population of long-tailed macaques have, for generations, used tools to harvest shellfish. And in Brazil, researcher Vedrana Slipogor plays videos to some of the world's tiniest monkeys - common marmosets – as she tries to understand the subtleties of primate personality. In Madagascar, drones mounted with thermal-imaging cameras might be the key to protecting some of the world's most elusive lemurs. And in the rainforests of Tanzania, we witness the moment when primatologist Dr Russell Mittermeier becomes the first person to have seen every type of primate on the planet.