Alison travels to Vietnam on a ground-breaking project to release rescued golden-cheeked gibbons Merry and Lee into their natural habitat. But before the pair can be set free, they have to be radio-collared, and this proves difficult when Merry refuses to co-operate.

The male capuchins explore their new outdoor enclosure for the first time, Hananya shows everyone who is boss at feeding time, and baby woolly monkey Diego plucks up the courage to join his family. Meanwhile, the keepers are overjoyed to discover golden-cheeked gibbon Zoey is pregnant again.