Paddington is happy with the life he leads alongside the Brown family, and he is popular among the neighborhood’s citizens who are emotionally supportive in various ways. To buy a unique book and give her aunt Lucy for her 100th anniversary, Paddington performs a number of small jobs and tightens the money she receives. When he finally gathers enough, he realizes that the book has been stolen and follows the responsible, but he escapes, and Paddington is unfairly accused and arrested for theft.
Although no one close to him believes he is guilty of theft, he is accused and condemned because there is no evidence of the alleged thief’s existence. While in jail, Paddington has many inmates, including the temperamental Nuckles who hired Paddington to be impressed by his recipe of marmalade sandwich. The Brown family is trying to prove Paddington’s innocence and scatter sketches with the description of the real thief.
Meanwhile, the thief uses the book to find a series of clues that he thinks will lead him to a great secret treasure. During all this time trying to wash out Paddington’s reputation, a riddle tells them that the stolen book leads to a hidden treasure of the one who wrote it. With Paddington inside, the penitentiary becomes a calmer place and the air more breathable, but the bear tries to stay optimistic even if the Brown family still fails to get him out of there.