As the freshness of spring arrives, Craig Mather as Mole finds himself completely losing patience with the tedious nature of his spring cleaning. Driven by a desire for adventure, he decides to abandon his underground dwelling and venture toward the river. It is here that he encounters Simon Lipkin as Rat, a water vole who spends the entirety of his days enjoying the river's serenity. The two quickly bond when Rat invites Mole for a ride in his rowing boat, and after sharing a delightful picnic, an enduring friendship is born between them. Their peaceful afternoon is interrupted when Denise Welch as Mrs. Otter gate crashes their gathering while searching for her daughter, Emilie du Leslay as Portia, who frequently wanders off in her quest for food. During their conversation, Rat and Mrs. Otter provide Mole with a stern warning regarding the dangerous inhabitants of the Wild Wood and introduce him to the concept of the wise, albeit solitary, Gary Wilmot as Badger who resides there.
Enter Rufus Hound as Mr. Toad, a character who is undeniably rich, jovial, and kind-hearted, yet suffers from being aimless and incredibly conceited. Toad is known for his erratic behavior, as he regularly becomes obsessed with the latest fads only to discard them just as quickly. At the moment, his obsession is boating; he zooms past the group's picnic on a high-speed wager-boat, embodying the philosophy that:
> Speed is of the Essence
As the swallows arrive to signal the start of summer, Mole and Rat accept an invitation to visit Toad Hall. By the time they arrive, Mr. Toad has already abandoned boating in favor of a new craze: a horse-drawn caravan. While the willing Mole is excited, the reluctant Rat is less convinced. During an overnight stop by the roadside, a passing motor car frightens the horse, causing the caravan to flip over. While Rat and Mole are left upset by the accident, Mr. Toad is instantly infatuated with the motor car. He acquires a racer and begins to terrorize his neighbors, most notably a family of anxious Hedgehogs. The local animals are left in a state of both fascination and dismay as Toad enthuses about his new passion, right up until he inevitably crashes the vehicle.
As autumn approaches, Mole becomes determined to save Mr. Toad from his own impulsive nature. He insists that he and Rat venture into the treacherous Wild Wood to seek the assistance of Badger. When Rat refuses out of fear, Mole bravely sets out on the scary road alone. He finds himself pursued by Neil McDermott as the Chief Weasel and his band of Wild Wooders, barely escaping when Rat has a change of heart and comes to his rescue. However, the two friends become hopelessly lost as fallen leaves obscure their path. After Mole suffers a minor injury on a boot scraper, they realize they have accidentally stumbled upon Badger's doorstep. While Badger welcomes them inside, the Chief Weasel is simultaneously plotting with his gang to steal Toad Hall so they can live a life of luxury. In the chaos, the food-seeking Portia is kidnapped by the gang.
Inside the warmth of Badger's home, Mole and Rat successfully convince Badger to help Mr. Toad. The trio arrives at Toad Hall only to discover that Mr. Toad has already ordered yet another car following his previous crash. They decide to confine him to his bedroom for his own safety until he regains some common sense. Their efforts are complicated when Mrs. Otter arrives, pleading for help to find her missing daughter. While Mole stays behind to guard the bedroom, Rat and Badger join the search for Portia. However, by feigning illness, Mr. Toad manages to escape Toad Hall and steals a magnificent new car, only to be caught by the owner and the police.
The subsequent court scene is a farce, with the Wild Wooders serving as the jury. Their goal is simple: ensure Toad is imprisoned so they can seize Toad Hall for themselves. Despite the gravity of the situation, Toad recounts his exploits in a grandiose manner, ignoring the pleas of Rat, Mole, and Badger for him to show true remorse. Consequently, Mr. Toad is sentenced to twenty years in prison.
With Toad behind bars, the Wild Wooders officially take over Toad Hall, where they begin fattening up Portia for a future feast. In prison, Toad manages to win the sympathy of the Gaoler's Daughter, who assists his escape by disguising him as a washerwoman. Meanwhile, Rat and Mole reflect on their friend's imprisonment while passing by Mole's abandoned home. Realizing that Mole never returned to finish his spring cleaning, they hold a humble feast, and Mole speaks fondly of his dwelling. They are briefly visited by the wassailing mice who wish the forest animals well. The peace is broken when Badger arrives with the news that Mr. Toad has escaped. Knowing the Wild Wooders will kill Toad if he tries to reclaim his home, the trio rushes to find him.
Toad's escape is fraught with peril. After being kicked off a railway engine by the law, he hitches a ride on a horse-drawn barge while still dressed as a washerwoman. After a failed attempt at laundry and a physical altercation with the barge-woman, he is thrown overboard. Soaked and desperate, he flags down a car—which happens to be the very one he stole. The owner, fooled by the disguise, lets him drive. Once behind the wheel, Toad's passion returns, and he drives furiously. Upon revealing his true identity, a struggle ensues, and the car crashes once again.
Eventually, Badger finds Toad at the gates of Toad Hall and informs him that the weasels and stoats have taken over and are holding Portia captive. Mole manages to trick two guards into believing an attack is imminent, allowing the group to utilize a secret tunnel known to Badger. Badger, Mrs. Otter, Rat, Mole, and Mr. Toad launch a surprise attack on the unsuspecting Wild Wooders during a celebratory party. After a fierce fight, the friends reclaim the hall and rescue Portia.
As spring returns once more, the animals work together to restore their home. Rat and Mole find contentment in their quiet friendship on the river, preferring their peaceful bond over Toad's chaotic adventures. Mr. Toad throws a grand party to celebrate his return, but his dramatic entrance—via an airplane or jet pack—proves that despite everything, he has not changed his ways in the slightest.
