HASEEN DILLRUBA is the story of a wife accused of murdering her husband. Rishabh Saxena aka Rishu (Vikrant Massey) resides in Jwalapur along with his mother Lata (Yamini Das) and father Brijraj (Daya Shankar Pandey). He is looking for a girl for marriage and his search leads him to Rani Kashyap (Taapsee Pannu) in Delhi. Rishu falls for Rani instantly. Lata realizes that Rani is not the simple and homely girl that she's looking for. But Rishu is adamant. The marriage takes place. A nervous Rishu fails to consummate the marriage. Lata, meanwhile, starts chiding Rani for lying that she can cook.
One day, Rishu overhears Rani speaking to her mother (Alka Kaushal) and her masi (Puja Sarup) that Rishu is not good in bed. Rishu is hurt and retreats into a shell. Rani gets lonely. One day, Rishu's cousin Neel Tripathi (Harshvardhan Rane) comes to stay with the Saxena's. Neel is dashing and well-built and Rani gets charmed by her. Neel realizes that Rani is attracted to her and both begin a fling. Rani falls in love with Neel to the extent that she begins to learn cooking so that she can feed him his favourite dishes.
One day, Neel expresses the desire to have mutton. Rani, who's a vegetarian, agrees and goes out to buy meat. The same day, she tells Neel that she'd like to end the marriage and move in with him. A commitment-phobic Neel panics and runs away. Rani is hurt and she blurts the truth to Rishu. Rishu wanted to have a fresh start but this confession hurts him even more. A few months later, an explosion takes place in the Saxena residence, killing Rishu. The investigating officer, Kishore Rawat (Aditya Srivastava), is sure that Rani has killed Rishu. What happens next forms the rest of the film