"The Christmas Box" is a heartwarming film based on the novella by Richard Paul Evans. The story follows a successful businessman, Josh, who, along with his wife, Emily, and their daughter, Annie, moves into an old house. They discover a mysterious box in the attic that contains letters from a woman named Mary to her deceased daughter, revealing her deep love and longing. As the family learns more about Mary's life, they begin to reflect on their own relationships and the true meaning of Christmas. The film emphasizes themes of love, loss, and the importance of family during the holiday season.