Joy dies after she gives birth to her daughter, leaving Wendy to raise her as a single mother with the help of Yeri, Wendy's sister. Their daughter grows up treasuring the letters her mother wrote for her to receive on her first ten birthdays. On her tenth birthday, she reads the last and most important letter that Joy left her; it tells the story of Wendy, Joy, and Irene when they were young college students.

But the end of one story only means the beginning of another. Now, at the request of her mother, Wendy and Joy's daughter must find a way to reunite Wendy and Irene, who have become estranged. Nothing is ever as easy as it seems, though, especially when it comes to things happening in the heart.