After the highly successful Raajamaanickam and then Chotta Mumbai (which too was a hit), director Anwar Rasheed gets ready with his third film, Annan Thambi. The film, scripted by popular scenarist Benny P. Nayarambalam, tells the story of two brothers Appu and Achchu, the sons of Ravunni, a ballet artist. While Appu is noisy and talkative, Achchu is forced to remain silent as he is born dumb. These differences between them has resulted in hostility brewing between them and hence their father has to separate them in earlier years itself, bringing them up in two different places.
Appu grows up in Pollachi, and is always ready to clench his fists and fight as and when required. He and his gang of friends are always in the middle of one boisterous activity or other. Achchu is with his father in Palakkad, as the main artist in his father's ballet troupe. He is a do-Good, always ready to help people out. The two brothers grow up as enemies, but their friends and all those around them want to see them united as loving brothers.