Pratha and Raghav met in college and fell in love. Pratha didn't know and still doesn't know there is a ghost of woman who was married to one of Pratha's ancestors, and since he was unable to keep her happy, she cursed him that no woman in his family would have a happy married life (then she committed suicide). The ghost is after Pratha to make her life a hell especially because Pratha is supposed to look just like the woman the ghost's husband was in love with.
On the day of their wedding, Raghav's real mother (Raghav thinks this woman is his aunt and not his mother) finds out about the curse and then is now trying to save Raghav (but she doens't tell anyone else, not even Raghav and Pratha). The woman he thinks is his mother did not want the wedding to happen becuase Pratha's mother (who died) had said that Pratha was ashubh. She now sees bad things happening in the house, and just wants Pratha to leave.
The Ghost has tried to kill RAghav, and is trying to hurt Pratha. Ambika (his real mother) tells the ghost that she will make Pratha's life a hell so that the ghost will stay away from Raghav and not hurt him.