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.