Alison travels to Vietnam for a ground-breaking project. Two rescued gibbons are to be released into their natural habitat, but will they have the courage to leave their old lives behind?
It's graduation day as baby golden-cheeked gibbon Mikado moves in with his new foster mum Alex, full time, and geriatric stumpie Gerald is rushed to the operating theatre.
The staff prepares for two new woolly monkeys from Switzerland, and the male capuchins are put to the test with a clever puzzle feeder.
Staff are anxious as chimp Athena undergoes an eye operation and woolly monkey Piquita's baby is finally given a name.
Chimp Ben's mysterious infection has spread to some of the others in his group, and it's a race against time to diagnose and treat it effectively. Meanwhile, the orang-utans are watching their weight, but are not so keen to get onto the scales.
Chimp Ben has a nasty infection and animal director Jeremy is worried it may lead to him losing his foot. Elsewhere, golden-cheeked gibbon Tien has undergone a transformation, and keeper Holly checks up on Xuzy.
There is a scuffle between the female capuchins, Tia needs surgery, and orang-utan Amy is heavily pregnant - and very grumpy. Meanwhile, there is something new in the play area of the chimp nursery, and Alison has her last visit with Paulo.
Baby woolly monkey Paulo is tempted outside by some delicious bugs, while onions are used to encourage natural behaviour amongst the capuchins. The team also has a radical plan for the third meeting between youngster Ben and alpha male Hananya.
Pregnant woolly monkey Piquita looks fit to burst, capuchin Sean, over from Chile, is keen to prove that nobody can groom quite like he can, and life hangs in the balance for Blue the ruffed lemur.
Mad Max meets his new housemates, and chimps Ben and Pip are in shock after another meeting with Hananya. Over in the woolly monkey enclosure, Piquita is the centre of attention and, in Paddy's chimp group, Bart enjoys his first taste of honey.
Baby woolly monkey Paulo meets his new family for the first time, young chimpanzee Eddi has fun and games with baby brother Bart, pregnant orang-utan Amy gets to grips with a breast pump, and Mad Max the marmoset arrives at the park.
As Zoey the golden-cheeked gibbon goes into labour, the various gibbons in the park seem to know that one of their number is giving birth and have a morning sing-off.
A baby chimp tries to prove he is grown up enough to go it alone. The Bachelor Boys' reputation, meanwhile, takes a hit when they become frightened of a new toy.
A big decision must be made when alpha male Hananya continues to exhibit violent behaviour. Chimps Simon and Eveline, meanwhile, compete in a swing-off and there is some dental surgery to be done.
Resident capuchin TJ joins the new Chile arrivals, but he seems to be in a mischievous mood, and Alpha male chimp Paddy has to step in and keep his unruly troop in line. Elsewhere, orangutan Amy is pregnant.
Hananya shows that he is not so tough when it comes to needles, while four-month-old woolly monkey Paulo is being hand-reared by Mike and Alison. Elsewhere, the other chimps enjoy a `banana-fishing' expedition.
The team are forced to step in when the chimp introduction goes wrong and Ben is injured by the alpha male, orang-utan Hsiao-Quai struggles with her ever-growing son Kai, and the park's staff prepare to welcome another baby orang-utan into the fold.
Wildlife vet John Lewis is given a run for his money when he tries to sedate two excitable chimps. Plus, the male capuchins get used to life together.
Eighty-eight capuchin monkeys rescued from a research laboratory in Chile wake up to their first morning at Monkey World. Rodders has a run-in with a sticky melon, and Seamus the chimp comes face to face with alpha male Butch.
Alison looks forward to the prospect of baboons being at the park, while recently arrived marmoset Clyde, rescued from the pet trade, braves the great outdoors for the first time.