The series begins as Alison and Jeremy rescue two marmosets mistaken for capuchin monkeys in Liverpool.
Chaos reigns at the capuchin house when Winslow's group have a weigh-in. Meanwhile, there is dissent in the ranks when chimp Tikko appears to challenge Hananya for leadership.
Five-year-old Jin leaves home and joins the orang-utan nursery. Meanwhile, troublemaker chimp Bart is up to his usual mischief when Paddy's group are given sacks full of treats.
Alison and Jeremy head to Germany to collect a lonely stumpie called Floh. Back in Dorset, the chimp team suspects Cherri might be pregnant.
Chimp Tikko undergoes surgery when he gets a tooth infection, newcomer Floh meets leader Sam, and golden- cheeked gibbon Tien is on the look-out for a mate.
Alison agrees to take in a neglected marmoset. Baby Leo is brought to the park by the RSPCA and is in a dreadful state, leaving staff unsure as to whether he will survive.
Golden-cheeked gibbon Tien finally meets his new mate, Kim, but the course of true love does not run smoothly. Meanwhile, naughty chimp Rodders pushes Lulu to the limit.
Excitement is in store at Hananya's enclosure when chimp Cherri gives birth to twins. Elsewhere, woolly monkey Pacaja takes a shine to leader Oaska.
Gordon's orang-utans swap houses with Sally's chimps, but the task of switching habitats proves to be a mammoth operation involving the veterinary team and the primate care staff.
Everything changes for Lulu, Rodders, Ash, Brian and Sally, who now have other chimps living nearby. Meanwhile, baby marmoset Leo is finally well enough to meet his new housemates.
Hananya's chimps are subdued when Cherri loses one of her newborn twins. Elsewhere, a fight breaks out at the lemur enclosure when two new arrivals are given a rough welcome.
Alison and wildlife vet John Lewis travel to Monkey World's sister sanctuary in Vietnam to release two golden-cheeked gibbons back into the wild.
Alison heads to Cheshire to rescue four more marmosets. Meanwhile, the primate care staff build a special enclosure to keep baby woolly monkey Bueno Junior safe.
In the orangutan nursery, all eyes are on Hsiao-quai, who the keepers hope will step up to the mark and adopt the orphaned baby Bulu, who has just arrived from Hungary.
The rescuers face a heart-breaking dilemma when chimp Susie is taken to the hospital and found to have an inoperable heart condition.
Alison heads to the Maldives to rescue a slow loris that was confiscated during a drug raid. Back at the park, Jeremy is outwitted by capuchin.
Baby orang-utan Bulu receives a new room-mate in the form of six- week-old Rieke from Berlin Zoo. Meanwhile, the new marmoset house is finally set to open.
Bulu and Rieke keeo the team busy.