TAISH is the story of two families who end up destroying each other. Rohan Kalra (Jim Sarbh) is a UK resident of Indian origin who works as a GP in a hospital. He is living-in with Arfa Sayeed Khan (Kriti Kharbanda), who is of Pakistani origin. Rohan takes leave from work to be with his family in the countryside and to attend the wedding of his brother Krish (Ankur Rathee) with Mahi (Zoa Morani). Rohan wants Arfa to join him but he's apprehensive how his father (Ikhlaque Khan) would react on knowing that he's dating a Muslim girl. Arfa understands and stays back.
Rohan returns home and his mother (Monisha Hassen) tries to set him up with Simmi (Melissa Raju Thomas). Rohan's best friend Sunny Lalwani (Pulkit Samrat) too joins the celebrations, meanwhile. He also convinces Arfa to come for the wedding and even tells the truth about their relationship to Rohan's parents. All is going fine until one day the whole gang goes to a pub to celebrate.
Here, Rohan sees Kuljinder Brar aka Kulli (Abhimanyu Singh). He goes berserk and has to be taken home. Sunny is puzzled at the turn of events. To which Rohan reveals that Kulli had sodomized Rohan when he was 10 years old. Sunny is enraged. He goes back to the pub where Kulli is still present. He assaults him in the washroom. Kulli's life is saved but he loses his voice and ability to walk. Kulli's brother is the notorious gangster Pali Brar (Harshvardhan Rane). Pali is cross with Kulli as the latter has married the love of his life Jahaan (Sanjeeda Shaikh). But when he learns about Kulli's condition, he goes out all to find out who did it. When he realizes it is Sunny, Pali decides to take revenge. On the day of the wedding, he kills Krish. What happens next forms the rest of the film.