Paddington, a lovable bear living with the Brown family in Windsor Gardens, is now a valued and popular member of the community. His Aunt Lucy's 100th birthday is approaching, and Paddington wants to gift her a unique pop-up book of London, found in Mr. Gruber's antique shop. Paddington undertakes various odd jobs to buy the book, but it is stolen before he can purchase it. Falsely accused of the theft, Paddington is convicted and sent to prison. In jail, with his unfaltering optimism and kind-hearted nature, he makes new friends, including the initially fearsome but ultimately kind-hearted chef, Knuckles McGinty.

Meanwhile, the Brown family works tirelessly to clear Paddington's name and find the true culprit. They unravel clues that lead them to a charming yet unscrupulous actor, whose ambition has driven him to desperate measures. The Browns face numerous obstacles as they chase down leads and try to collect evidence. Through adventure, teamwork, and unwavering belief in justice, they endeavor to reveal the truth and ensure Paddington’s release from prison.