Years ago, Ah Fai's father, Cheung Wan On, had an illicit affair with Li Sa in which she wound up pregnant with Yat Siu. The father being a "little" man always afraid of confronting issues did nothing. Yet the grandfather, having found out about it, was sympathetic to her plight. He never told anyone the secret because he did not want to break up his son's family. He tried helping Li Sa out when she left for Shanghai, but eventually lost touch with her. This becomes a lingering regret of the grandfather's because he never did more for her and the unborn child.

Kuk Li Sa from the start realizes that "she" is the one Ah Fai was sent to find, but she had changed her name and had long moved out of the neighborhood that they were searching. With her relatively happy and stable life as the head of her own tea restaurant and ill feelings toward the irresponsible man that left her, she hides the truth from the two brothers. In one of the series most comedic moments, Ah Fai who Yat Siu has just invited to stay overnight in their Shanghai flat accidentally knocks over the broken picture plate of Yat Siu's father. As the two young men work to piece the plate back, Ah Fai offhandedly remarks how familiar the eyes were, not realizing that it was actually an old picture of his own father. In duress, Li Sa scolds them frantically to not touch her things, especially her dead husband. Up until that point, Li Sa had always come across as a very nice and soft-spoken mother figure who never raised her voice, so everyone is taken by surprise at her odd reaction. In the end, Yat Siu does find out her secret and goes to Hong Kong to visit the other family he never got to know.