Daag is the story of a man wrongly convicted of murder, on the run from the law.
Sunil (Rajesh Khanna) is forced to leave behind his new bride Sonia (Sharmila Tagore), when he kills her would-be rapist.
In an attempt to establish a new identity Sunil meets Chandni (Rakhee) and ends up marrying her to give her child a fathr's name.
A chain of events brings together Sunil and Sonia but the long arm of the law also catches up with him.
on not just a murder charge but also his marriage of convenience, which is interpreted as bigamy.