Kehta Hai Dil is the story of a family who lives in the small, idyllic town of Anand Nagar. It the family of SP Aditya Pratap Singh, Dr Jaya Singh and their three children - Karishma, Kunal and Kiran.
But primarily, it the story of Karishma and how the dramatic events that occur in her life affect the entire family.
Karishma, a young college-going girl, is in love with Dhruv, but her family disapproves because they feel she is too young. Aditya's arch-enemy is the Mayor of the town. The Mayor's wife, who is the main brain behind all the villainy, takes the opportunity to use Karishma as a pawn in her war against Aditya. And for this she takes her son, Nikhil's help.
Nikhil pretends to be a great friend of Karishma's, even promising to help sort things out with Dhruv. He is extremely sweet to her. Whenever she is low, he cheers her up.
He earns her trust and one night, pretending that he wants her to meet his parents, take her to his parents' farmhouse, where a party is on. He tricks her into staying back after all the guests have left. The press, who has been informed by Lalita, arrive there and find Nikhil and Karishma in an ostensibly intimate position.
The news is splashed all over the press. Lalita is very proud of Nikhil and we realise that Nikhil is a bad guy after all.
Karishma also realises that Nikhil had been playing with her all along. However, since the press has carried her photo coming out of Nikhil's house, the only way she can save her family's face is by marrying Nikhil.
The wedding is fixed. Karishma pretends to be very very happy. She is completely immersed in the wedding preparations... the clothes, the jewellery. She is going to leave behind the home she grew up in, her family and go to the house of the man she loves. There will be beautiful moments between mother and daughter. Dhruv is also present at the wedding. Seeing Karishma so happy, makes Dhruv happy and sad at the same time... happy because she looks so radiant, and sad because he still loves her. But he loves her enough to let her go to the man she loves.
Nikhil treats Karishma very shabbily. He says that he might have married her, but he doesn't want her. Lalita is the main villain in the picture. Nikhil will listen to anything Lalita says and Lalita is the one who instigates him into treating Karishma badly. Her motive is to drive Karishma out of the house so that Aditya and family will be ruined.
We see Karishma go though hell. In front of her parents, in front of society she pretends to be a happy wife and bahu. But in her private moments, we realise what a difficult, torturous time she is having. It makes us respect this young girl tremendously for her extraordinary courage.