A wealthy American named Jervis Pendleton, while on a trip to France, stumbles upon an orphanage and becomes captivated by the spirit of a young French girl named Julie. Struck by her potential and vivacity, Jervis decides to sponsor her anonymously, providing funds for her education and a prestigious college in America. As a gesture of gratitude, Julie writes letters to her unknown benefactor, whom she calls "Daddy Long Legs" because she has no other name for him. Despite signs of luxury in her benefactor's life, she imagines him to be an old and kind man.

As Julie settles into her new life in America, she excels academically and is warmly embraced by her peers. She exchanges numerous letters with her mysterious benefactor, painting a vivid picture of her growth and experiences during her college years. Without revealing his identity, Jervis becomes deeply invested in Julie's development, finding himself visiting the college under the pretext of business to catch glimpses of her progress. The correspondence between them grows more personal, hinting at feelings that neither understands fully yet. The story unfolds as Julie's affection for her unseen benefactor blossoms, creating an intricate web of emotions and expectations that set the stage for future revelations.