Sadak 2 is the story of a girl trying to expose a powerful godman. Aryaa (Alia Bhatt) has lost her mother Shakuntala to cancer but she feels that it's because of the involvement of a godman Gyaan Prakash (Makarand Deshpande). Her father, Yogesh Desai (Jisshu Sengupta) is a devout follower of Gyaan Prakash and he fails to realize the truth. He even gets married to Shakuntala's sister Nandini (Priyanka Bose), also a follower of Gyaan Prakash.
Aryaa meanwhile starts an online campaign against this godman and gets close to 2 lakh followers. It also helps her meet Vishal (Aditya Roy Kapur) and both soon start a relationship. All is going well but one day, Gyaan Prakash attempts to kill Aarya by sending a henchman. Vishal, however, kills the henchman for which he's jailed. Aryaa is sent to a mental asylum and falsely declared mentally ill. Her online activities are also ceased.
She, however, escapes from the hospital and decides to go to Mount Kailash. This is because her 21st birthday is round the corner and her mother had wished that she visit this holy place on this important day of her life. She books a cab three months in advance from Pooja Travels and Tours, run by Pooja (Pooja Bhatt) and her husband Ravi (Sanjay Dutt).
After Pooja accepts the booking, she dies in a road accident. Ravi is shattered and turns suicidal. This is when Aryaa lands up at his place and demands to go to Ranikhet from where she's supposed to take a chopper to Mount Kailash. Ravi reluctantly accepts the booking, because of Pooja's reference. The journey begins and both end up telling each other about the sorrows of their lives. Incidentally, Vishal, too, gets released from the prison and he also joins in the journey. Unfortunately, Gyaan Prakash's men catch up with the trio. The godman sends his most devoted disciple, Dilip Hathkataa (Gulshan Grover), to finish them off. What happens next forms the rest of the film.