Ab...Bas! is a thriller movie in which Somiya Mathur lives a middle-class lifestyle with her dad and mom in Mumbai. At the age of five her parents go through a bitter divorce and she moves out to live with her mom.
After she matures, her mom passes away, and she swears never to see her dad again. She rents a room with a middle-aged couple, who she calls 'Aai' and 'Baba', and is friendly with Niti, who runs a restaurant. Somiya decides to enter in a beauty contest, competes, and is crowned the city's beauty queen. This gets her unwanted attention from a strange male, and a wealthy bachelor, Karan Malhotra, comes to her rescue.
Both fall in love with each other and get married. They live an idyllic, wealthy, and harmonious lifestyle, and a few years later they become parents of a girl, Sarah. When Sarah is of school-going age, Somiya gets a phone call from a woman named Ruby, passionately asking for Karan's company. When she questions Karan, he readily admits to having an affair with her but promises to not have to do anything with her again.
The next day she smells another woman's perfume on Karan's clothes and when confronted, he assaults her. The abuse continues and he forbids her to leave the house. She seeks the help of Niti and her former landlords, and manages to escape. An enraged Karan hires goons, advertises in the newspapers, as well as seeks the active cooperation of his Police Inspector friend, Bhaskar Shetty, and he knows it will not be long before he finds his highly visible, attractive 5'10" wife and daughter.