TADAP is the story of an obsessed lover. Ishana (Ahan Shetty) lives in Mussoorie with his adopted father who is addressed by everyone as Daddy (Saurabh Shukla). Daddy is a close aide of Damodar Nautiyal (Kumud Mishra), a politician who is fighting the state elections. Ishana runs a theatre and helps Daddy and Damodar in political activities.
On the day of vote counting, Damodar's daughter Ramisa (Tara Sutaria) returns from the United Kingdom where she is studying. Damodar wins the elections and when Ishana is celebrating the former's victory, Ramisa spots him. She gets attracted to him. Soon, she befriends him and even confesses that she is attracted to him. Ishana falls crazily in love with her.
One day, she tells him that Damodar is compelling him to get married. She assures Ishana that she will convince her father to change his mind and that they should not meet for a few days. She kisses and leaves him and at that exact moment, Damodar sees them. He and Ramisa's grandmother decide to separate the lovers and teach Ishana a lesson. What happens next forms the rest of the film.