Life is a Kasauti .............. a test stone and our passage through it a test of our ability to lead a meaningful life. Only those who pass this test leave their mark on this proverbial test stone.
Sapna (Hema Malini), a slum dweller of Bombay seeks refuse from her ever quarrelous environment and from the drunken outbursts of her foster father (Satyen Kappu) in the Company of Childhood friend Neeta (Sonia Sahani). Neeta works for Heera (Ramesh Deo), a playboy smuggler, who soon enlists Sapna also as Carrier and finds in her a fresh flower to be plucked for his sensuous pleasures.
Amit (Amitabh Bachchan) an educated and happy go lucky Taxi driver saves Sapna from the clutches of Heera but soon she is accused of attempting to kill her foster father. Amit leaves no stone unturned to prove her innocence. Sapna is sent to prison for six months. This is too much for her mother (Sulochana) and in a fit of anger she kills Sapna's foster father. Amit visits her inside the prison and promises her to marry Sapna on her acquittal........ but on the eve of their marriage Amit's father (Murad) refuses to accept an ex-convict as his daughter-in-law. Not wanting to break up his family, Sapna quietly walks out of Amit's life.
Amit and Pyarelal (Pran), a loyal friend of Amit who had adopted Sapna as his sister, frantically searched her but their search is of no avail as Sapna had already left the city.
At Calcutta Sapna becomes an instant hit on the stage through Ashok Babu (Vijay Sharma), a reputed impressario.
At long last, fate smiles on Sapna. She is grateful to Ashok Babu for all that he has done for her. One day Ashok proposes to her.
And then what happens ?
Does Sapna climb down from her ladder of fame and success and return to her poor past? or does she marry Ashok and apt for a life of luxury?
For answers to all these questions see Arabind Sen's "KASAUTI".
(From the offical press booklets)