Kaadhal movie revolves around Murugan (Bharath) who is a diligent scooter mechanic in Madurai and life goes on smoothly for the young man till the rich schoolgirl Aishwarya (Sandhya) sets her eyes on him. The infatuation reaches dangerous levels when she coaxes Murugan to take her away from the clutches of her family, which has other plans about her future.
The naïve Murugan hesitantly yields to her charm and the two run away to Chennai. Murugan's friend Stephen (Sukumar) helps them in the hour of crisis and the lovers unite in marriage. But her family is not going to give up so easily on the daughter they dote on.
The family tracks down the couple that has eloped and eventually separates them. Aishwarya agrees to marry another man in order to save Murugan's life after he is being beaten by her father.
While she believes this decision is best and moves on with her life, she one day while on the road with her husband and daughter runs into Murugan who was suffered permanent brain damage.
Knowing that she had made a mistake and not knowing how to undo the sins of her father, she and her husband decide to take care of Murugan.