Santosham is a Romance with family based movie in which, Karthik (Nagarjuna) is a well-placed architect in Ooty. He falls in love with Padmavathi (Gracy Singh), an IT intern. Padmavathi takes her own sweet time to accept Karthik's love. Padmavathi has a cute cousin sister Bhanu (Sreya). Bhanu encourages their love and gives courage to Padmavathi. When Padmavathi reveals about her love, her father Rama Chandraiah (K Viswanath) resists and asks her to marry the guy he has chosen for her. Padmavathi flees from home and marries Karthik. Padmavathi is very eager to get back to her parents and get their blessings. But Rama Chandraiah keeps them at bay. Karthik and Padmavathi migrate to New Zealand and they give birth to a kid named Lucky. Padmavathi dies in an accident.
Rama Chandraiah has a very big joint family. A few of the family members opine that inviting Karthik and his kid for a marriage to be happened at their place would give an opportunity to get a closer look at Lucky, the kid of Padmavathi.
Bhanu has fallen in love with Karthik at first sight way back when she went to meet Padmavathi at Ooty. At that time she was not aware that Karthik was the same guy with whom Padmavathi was in love. She meets Karthik, a widower now. She continues having feelings for him. But at the same time, there is Pawan (Prabhu Deva) - a childhood fiend of Bhanu - who is deeply in love with her.