Sphadikam movie is about the relation between the Father and the Son. Chacko Master (Thilakan) who is a high-school headmaster and who is a president's medal winner in Mathematics. He is a very strict teacher and emphasizes memorization and discipline at the expense of analysis and creativity in school. He punishes his students ruthlessly and gives no special treatment to his son Thomas (Mohanlal) who is also a student in his class. Chacko always assumes that his son is behind every mischief in class, and punishes him until the actual culprit gives himself in.
Unlike his father, Thomas isn't too good in math (he cannot memorize the binomial theorem) but he is very creative and productive in designing mechanical and electronic gadgetry like a mechanical school bell which his father destroys later. For instance, he impresses his mother and sister by developing an AM radio receiver inside a soap-case at a time when phonographs were more prevalent in his village. When his father finds out about the receiver he throws it into flames and destroys it; he forces his son to focus on his studies instead of being an inventor. Thomas works hard, and he does well in his language paper, but his dad asks his language teacher to grade his paper with no leniency, so that he gets a low grade. When he finds out that even his most beloved language teacher was biased against him he becomes outraged. He runs away from home.
Fourteen years later, he returns to his village. Thomas, by now, had changed into a totally different person. He was no longer interested in clockwork and gadgetry; he owned a stone quarry and had become a well known rowdy wanted by the authorities as a prime suspect in many unsolved crimes. His father still hated him and never accepted him as family. But as the film progresses, both father and son regret what they had done to each other. In an interesting turn of events the father and the son reunite in a very emotional way.