As the title indicates, Appa dwells on the role of fathers — how they bring up their kids becomes a deciding factor in their children's lives. Like some of his previous films, in this one, too, Samuthirakani touches upon a few socially relevant issues. To start with, there are three fathers — Dayalan (Samuthirakani), a humanitarian who has high hopes on society, Singaperumal (Thambi Ramaiah), a self-centered person who is concerned only about his ambitions, and Nadunilaiyan (Namo Narayana), a well-calculated man who always prefer to be on 'safe side' in life. The story kicks off when each o...