Christopher Robin, portrayed by Ewan McGregor, is on the verge of a significant change in his life as he prepares to leave for boarding school. To bid him farewell, his beloved friends from the Hundred Acre Wood—Winnie the Pooh, Tigger, Piglet, Eeyore, Kanga, Roo, Owl, and Rabbit—organize a heartfelt goodbye party. In a touching moment, Christopher reassures Pooh that he will hold onto their memories forever.
As the years roll by, Christopher transitions into adulthood, marrying the talented architect, Evelyn, played by Hayley Atwell. They welcome a daughter, Madeline, played by Bronte Carmichael, into their family. Christopher serves in the British Army during the tumultuous era of World War II. Post-war, he takes on the role of an efficiency expert at Winslow Luggage. However, the demands of his job lead him to neglect his family, igniting plans to send Madeline away to school.
The company faces dire financial straits, prompting Giles Winslow Jr., played by Mark Gatiss, to instruct Christopher to cut costs by 20%, primarily through staff layoffs. This stressful predicament leads Christopher to forgo a summer weekend retreat with his family at their cottage in Sussex.
Meanwhile, in the Hundred Acre Wood, Pooh awakens to find his friends absent and takes a brave leap through Christopher's door, landing himself in London. Surprised yet delighted by this unexpected reunion, Christopher brings Pooh home, leading to a comical sequence of events where Pooh wreaks havoc in search of honey. The following day, Christopher takes Pooh back to Sussex on the next available train.
As they venture into the Hundred Acre Wood, Christopher's patience is tested by Pooh's whimsical nature and fears of Heffalumps and Woozles. Their playful adventure takes a turn, leading to an argument where Christopher laments not being a child anymore and they end up separated in the fog. After becoming trapped in a "Heffalump Trap" that fills with rainwater, Christopher encounters Eeyore and Piglet, who guide him to their hiding friends. To prove his identity, Christopher pretends to vanquish a Heffalump, which ultimately leads to a joyful affirmation of their friendship.
The next day, in a rush to present his plan, Christopher dashes back to his job, leaving his old friends behind yet unable to share his experiences with his family. Realizing that Tigger mistakenly took Christopher's essential documents while drying his briefcase, Pooh, Tigger, Piglet, and Eeyore embark on a mission to return the materials to London. Along the way, they encounter Madeline, who recognizes them from her father's illustrations and joins their cause, followed by Evelyn upon discovering Madeline's note.
At the crucial meeting, Christopher discovers his briefcase contains only items from the woods, an oversight caused by Tigger. As Evelyn arrives, Christopher joins her in the search for Madeline. The group stows away in crates, and after some comical mishaps, they find themselves reunited near the Winslow building. Madeline's unfortunate fall results in the loss of important papers, causing distress not only to her but also to Pooh. Christopher reassures her of her significance, promising that boarding school is off the table.
In a moment of ingenuity, Christopher proposes a radical plan involving slashing prices, introducing paid leaves for employees, and selling directly to the public to stimulate demand. Although Winslow Jr. dismisses the idea, Winslow Sr. is intrigued and supports it, leading to a spectacular showdown where Christopher triumphantly highlights his rival's lack of contribution.
Ultimately, Christopher takes his family into the Hundred Acre Wood, welcoming all his cherished friends for a delightful reunion filled with nostalgia and joy.
As a delightful mid-credits bonus, the employees of Winslow's are depicted having a joyous time at the beach, accompanied by Richard M. Sherman performing “Busy Doing Nothing” on piano. Pooh, Piglet, Eeyore, and Tigger are seen soaking in the sun, with Eeyore humorously acknowledging, "Thank you for noticing me."
