Udayon movie revolves around 75 year old Suranadu Kunju and his son Papoyi ( Both are Mohanlal). Kunju thinks that the heartbeat of earth is in soil and not in maths. His beliefs on the land and agrarianism is good but his value system that farmers and farming is more important and better is not. He does not let his sons pursue there interest and wants them to do farming also. Which leads in they becoming negative towards father.
Also when he tries to marry off his daughter to an ugly but farming loving another narrow minded character instead of an educated handsome doctor makes them feel that the father is destroying and spoiling their lives with his stubbornness and high handedness. The presence of a villainous brother in law to his sister's son JCB (he drives a JCB played by Kalabhavan Mani) adds a twist as he interferes in the family property dispute.All said and done the sister doesnot want eveil to her brother (Mohanlal) and her younger son the mute also doesnot want.
Papoyi tries to save things but never has luck ultimately he tries and prevents many a bad scene but cannot prevent his youngest brother being killed and Kunju kills the villainous brother in law Perumal (Salim Ghouse) who does the evil deed and gives the family property keys to sister and the patriarch stick to Papoyi after the death of his youngest kid Ponnan.