Donald Turner arrives home in Rochdale fresh from graduating as a fully qualified Veterinary Surgeon, and takes up a position with grumpy older vet Maurice Webb. He is horrified to learn that the Great Northern Zoo is a part of the practice, especially when he is called out on Maurice's day off to treat a chimpanzee who has had a thumb bitten off. The vet is needed so that they can say they 'Called In The Experts'.
Donald and Maurice are called to the zoo when a female elephant is in extreme pain in her jaw, and is getting more and more debilitated and dangerous. Donald and Maurice discover that the elephant has severe arthritis and there just aren't the drugs to deal with it, and are forced to euthanase her. Donald is left in a black mood as he doesn't consider that he can help any of the animals at the zoo, with his limited knowledge.
Mr. Webb is very displeased when the newspapers learn about the elephant's death, but Donald decides to dig in and learn all he can when Rajah the tiger is poisoned by a disgruntled ex-keeper.
Donald goes on an interview for another job, and watches as Jenny mounts a newspaper campaign to keep the zoo open.
Donald decides to take the new job, but has some misgivings about leaving the zoo animals in Webb's care and Jenny is offered a position with a London newspaper.
Donald is called in to inspect the animals at a local circus and teaches an old seal trainer some new tricks, and he helps Paddy Reilly find some missing monkeys at the zoo.
Donald and a local physician team up for a house call on an eccentric old woman who needs medical attention as much as her pet monkey, and he travels with Maggie to the Continent to bring back an elephant for the zoo.
Donald treats an obstreperous macaw in the surgery, enlists Maggie as a nurse for a convalescing lion cub, and investigates suspected hoof and mouth disease at the circus.
Donald tries out his new anesthesia gun on a pack of wolves and on an orangutan who has miscarried but refuses to give up the corpse of her baby.
Donald joins Paddy and the police in a search for a wild cat reported to be running loose on the moor, and faces some dramatic changes in his personal life.
Donald is now well-known as a zoo vet, and is travelling the country dealing with circus animals, but still finds time to deal with the Great Northern Zoo's animals. The Northern Zoo itself is having a rough patch with Paddy acting as senior keeper and manager, and doesn'thold any illusions as to what is going to happen to the zoo. Maurice is annoyed about the amount of time Donald is away from the practice, and is even more annoyed when Donald informs him of a proposed safari park he will be involved with. Things finally come to a head when an elephant escapes from Ben Bishop's circus and injures a man, and forces Donald to split up the partnership.
Donald encounters a hostile lion trainer at the proposed safari park and is called in to treat three tiny alligators at a local night club.
Donald investigates the strange behavior and requests of an Italian couple with a trained dog act who are waiting out their quarantine at the zoo, and Ethel formally joins Donald at the safari park.
Donald helps prepare a dog for burial and meets an American dolphin expert.
Donald and Paddy battle a callous administrator as they struggle without much success to place all the zoo animals before the closing day.
Donald solves the riddle of vandalism in the village and an attack on a local vagrant, and provides a home for a laboratory baboon due to be put down.
Donald has trouble with the big cats:a lioness escapes, a tiger cub needs hand rearing, and a self-appointed expert insists on one to one contact with the pride.
Paddy and Donald settle the dolphins into a temporary home in France while Maggie tries to deal with practical problems at the park.
Maggie's a little prickly over the dolphin trainer Sindy but helps Donald cope with a mysterious epidemic running through the park's new lions.
Sindy and Donald journey to America to escort home the park's newest attraction-a killer whale named Cuddles.
Donald must learn quickly about the medical needs of killer whales when Cuddles begins losing blood, and he accepts some unusual help from the spirit world to treat a tortoise with inflamed eyes.
Donald has to find a suitable home for two baby elephants donated at the last moment by an old friend of Lady Anne, deal with all the confusion of the grand opening ceremonies for the safari park, and react to Maggie's intention to take a nursing job in the Middle East.
Donald and Paddy escort an orang-utan to a zoo, which later turns into a raging menace. Meanwhile a young eland with a tooth abscess attacks and kills it's keeper, and Donald comes under pressure from the press to put it down. Elsewhere a blind lady donates a mynah bird to the Bellington Zoo, where it is stolen by an underpriviledged boy from a nearby school.
A number of animals are killed at the Bellington Zoo and suspicions point to a keeper being responsible, it later transpires to be the work of a suspended prison officer who once worked at the zoo. Paddy is offered the post of head keeper at the Bellington and Liz masterminds an education centre at the zoo. Meanwhile Donald fights tooth and nail to prevent Challon using dubious methods to make money using the dolphins at Manford Safari Park.
Teddy Haslam accidentally shoots one of his hawks, while it is being stolen and takes it to Donald to save it, unfortunately Donald is not there and Ethel lends a hand, until Donald arrives. The education centre opens. A thief in the zoo turns out to be a young boy stealing money from the zoo pools and a pair of squirrels! Donald is called to see a miniature horse which has become the companion of a Llama, which unfortunately dies. Meanwhile at Manford Safari Park the tigers come down with a mysterious ailment which 'drowns' them. and needs all Donald's ingenuity to sort out. Which result in Donald and Challon being hunted through the enclosure by the big cats.
Whilst walking her dog across some wasteland, a young girl finds an abandoned orang-utan, which later is diagnosed as having hepatitis. Elsewhere there is an egg bound emu, escaped onagers and a heated exchange between a disreputable pet shop owner who sold the orang, and an angry Donald.
Donald is offered a job with animal entrepreneur Ben Friedhoffer. Meanwhile the Bellington Zoo is offered 3 black Panthers for a very low amount which makes Donald suspicious.
Liz is inadvertently poisoned by a number of poison arrow tree frogs that have been sent to the zoo instead of normal tree frogs. Paddy is devastated that he didn't check them first. Donald is called out what appears to be a Coypu at some local caves but instead turns out to be an Alligator.
On the eve of Ethe's wedding to Teddy, Donald is called to Madrid Zoo, where Shao-Shao the Giant Panda is showing signs of going into labour. A tearful Ethel asks Paddy to take his place in giving her away. After the baby panda is born he flies home to witness the marriage, to the delight of Ethel.