In Miracle on 34th Street, Susan's mother, Doris, is a no-nonsense woman who works as a special events director for Macy's department store. When their usual Santa Claus is intoxicated before the Thanksgiving Day parade, Doris hires an elderly man named Kris Kringle to take his place. Kris impresses everyone with his jolly attitude and seemingly magical abilities, such as speaking to children in their native language and knowing their secret wishes.
Susan is initially skeptical of Kris, especially when she overhears her mother tell a colleague that there is no Santa Claus. However, Kris begins to win over Susan and her mother when he takes on a more unconventional role as Macy's Santa. He advises parents where they can find better deals on toys and encourages shoppers to visit other department stores if Macy's does not have what they need. This strategy boosts Macy's sales and earns Kris a reputation as the best Santa in New York City.
However, Kris faces a major challenge when he is accused of being insane by the store's in-house psychologist, who believes that Kris truly believes he is Santa Claus. Kris is put on trial to determine whether he should be institutionalized, and he enlists the help of Doris's neighbor, a lawyer named Fred Gailey, to defend him. The trial becomes a media circus, with everyone in New York City taking sides in the debate over whether Santa Claus is real.
In the end, Kris's case is decided in a dramatic way that both proves his sanity and rekindles the Christmas spirit in those who witness it. The film concludes with Susan and her mother celebrating Christmas with Kris and other friends, and Susan's faith in the magic of Christmas fully restored.