As the title suggests, Kal Aaj Aur Kal talks about the changing times and the need to adapt to it. Ram Kapoor, a wealthy industrialist, calls his father Diwan Bahadur Kapoor to stay with him. Ram's son Rajesh who is good at heart, initially takes a liking to his grandfather but as the grandfather begins to impose his orthodox beliefs on the household, Rajesh rebels. As a last straw, Diwan Bahadur Kapoor, arranges for Rajesh's marriage with the daughter of an old confidante of his forcing Rajesh who is already in love with someone else to protest. Things come to such a passe that Ram Kapoor decides to go missing for a few days to provide his father and son adequate time to sort out their differences. Will this decision of Ram Kapoor have any effect on Diwan Bahadur and his grandson Rajesh?