Alison Cronin visits Dao Tien, Monkey World's sister centre in Vietnam, which was founded in 2008, and has since become the site of a pioneering rescue and rehabilitation mission for golden-cheeked gibbons. Here, the team faces trouble during an attempt to save a rare silver langur monkey, and director Marina asks human doctors to perform ground-breaking eye surgery on a gibbon.

Alison goes to great lengths when Trudy falls victim to a mysterious condition. Marcel the marmoset demonstrates small monkeys can be as clever as the larger apes, and baby woolly monkey Diego is allowed to join the adults.