George Mottershead lives in the flat above his father Albert's grocery shop with his wife Lizzie and their daughters Muriel and June. He suffers from post-traumatic stress disorder following his time in the army during World War I, but his mother Lucy is frustrated that George still lives with them and wants him and his family to move out. The family become concerned for George's mental state when he visits the local dockyard's quarantine office and purchases a squirrel monkey and an eclectus parrot which were about to be euthanised. George promises to sell the animals to a circus, but ends up buying an old Bactrian camel which the circus' ringmaster planned to slaughter. The three animals are kept in the family's small backyard, and while the neighbours are willing to pay to see them, the grocery shop gets fewer customers.

The Mottershead family struggle to adjust to their new life, while George continues to develop the zoo (which he names "Chester Zoo") and acquires more animals, including two goats, a pelican and several small birds for an aviary. He visits Matlock, Derbyshire, where the owner of a pleasure garden offers to sell him two Asian black bears, but when George tells the family about the offer, Lizzie, Muriel and Lucy refuse to let him bring them to the Manor. Despite this, George still returns to Matlock to collect the bears, accompanied by Lizzie's brother Billy Atkinson. While he is away, Lizzie visits Chester Council and tries to file for planning permission to build the zoo, while also making changes to George's plans for the zoo's layout.

As word spreads about the zoo, the Mottershead family are met with harsh backlash from the people of Upton, who are strongly opposed to the idea and start a campaign to prevent the zoo from opening. However, George is undeterred by the criticisms and appears at a town meeting to promote the zoo, but the villagers are unconvinced and the Mottersheads gain a bad reputation in the village, leading to June being bullied at school. Despite this, George writes a letter to Chester Council detailing their plans and starts digging a trench to surround the bear enclosure, while Albert and Muriel complete an aviary built around an old gazebo and transfer all the small birds into it. Local shopkeeper Mrs Radler visits Katherine Longmore and tries to convince her to side with Upton in the debate, but Katherine disregards her and continues to show support for the Mottersheads. At Chester Council, Ronald Tipping receives George's letter, but decides not to read it.

Discovering that one of the bears has escaped, George heads out to look for it. He finds the bear in a nearby forest, but the arrival of Billy's van scares it and it scratches George's arm. While he and Billy successfully get the bear back to Oakfield, George realises the zoo needs more money to make the enclosures more secure, and the next day he requests a £300 loan from the bank, but is refused. At the bank, George meets aristocrat Lady Goodwin, who takes a liking to Mortimer the squirrel monkey. She visits Oakfield to see Mortimer again, and George suggests she pay the Mottersheads a small amount of money per month to "adopt" the monkey. Meanwhile, Mrs Radler and Reverend Webb organise a petition to get the zoo closed.

The Mottersheads are left devastated by the news that planning permission for the zoo has been denied. To keep up with their debts, George and Lizzie sell one of the black bears to Belle Vue Zoo. Lucy notices the other bear acting strangely and realises it is pregnant. A land agent offers to buy Oakfield Manor for the same amount the Mottersheads bought it for, but George turns him away. At Chester Council, Frankie takes a copy of the Upton petition from Ronald Tipping's desk and has Billy take it to George. Reading through the reasons listed in the petition, George learns that Mrs Radler manipulated the villagers into making up false reasons for the zoo to be closed. He goes to Chester Council and confronts Tipping about the corruption, and while Tipping confidently disregards him, Frankie explains that the Mottersheads can legally appeal against the council's decision.

Albert discovers that the zoo's aviary has been vandalised in the night, and all its birds have flown away. George and Lizzie have a meeting with lawyer Neville Kelly, hoping for him to represent the Mottersheads in the upcoming hearing. Kelly during that meeting, if the telephone rang, picks up the receiver and puts it back at once to stop the ringing, instead of having a secretary to answer the telephone while Kelly is busy; that does not bode well to George for his chances of later contacting Kelly by telephone. However, Kelly's demeanour annoys George so much that he decides to represent the family himself. As the hearing draws closer, George spends many hours researching legal information and becomes more hostile and aggressive towards the rest of the family. June invites her school friend Barbara around to Oakfield and they play hide and seek, but when George catches Barbara in his study he is outraged and sends her home. Katherine agrees to be a character reference for the Mottersheads at the hearing. Realising George's short temper may work against them, Lizzie goes back to Kelly and asks him to be their lawyer, and he accepts. When George learns of this on the day of the hearing, he leaves and sits outside while the hearing takes place.