The film opens with Ved (Ranbir Kapoor) and Tara's (Deepika Padukone) monotonous back stories as people in the corporate world. A flashback shows, as a child in Shimla, Ved is fascinated by the stories narrated by a road side story teller (Piyush Mishra) who keeps mixing up his characters.
The film moves to real time where Tara meets adult Ved, while both are holidaying in Corsica. They come up with an amusing verbal pact to keep their real identities undisclosed. They explore the island together. They pretend to be "Don" and "Mona Darling" and talk in filmy dialogues. When she realizes she is falling in love with Ved, Tara decides to leave Corsica despite the romantic friendship with him. The story flashes back to young Ved who questions the story-teller about the reason for happy times ending quickly and notices each story has a sad the episode in it.
Tara returns to Kolkata, India. Tara's father (played by Nikhil Bhagat) hands over his tea business to Tara, she expands it by starting a line of tea boutiques, taking the company ahead. She is off to Delhi for work and four years have passed. One day, Tara surprisingly meets Ved, who is now a product manager. They reveal their original identities. They plan for a date at a Japanese restaurant. She expects him to talk like the days in Corsica but Ved talks about business. She calls Ved up home to be intimate. Ved leaves for his home and next morning Ved wakes up on time, completes the morning chores, wipes the car, ignores the transgender on the way, lets a female colleague into the lift—all this happens on his way to the office. He fixes a plan for meeting Tara again in the evening. Each morning to evening, similar incidents repeat monotonously. On Ved's birthday, he proposes to Tara but she is unhappy with the real-life Ved. She declines the proposal. Ved leaves his home by an auto-rickshaw. The driver (played by Ishteyak Khan) narrates how his dreams of becoming a singer were crushed. Ved breaks down and his residual mental disorder is triggered.
An exacerbated Ved due to his psychotic break, ends up upsetting his boss with a nonsensical presentation in a business meeting. Ved begs Tara to come back to his life. She indirectly informs him she is fixated on Ved's divergent personality from Corsica, not the matured Ved who lives by societal conventions. Later Tara expresses her realization of hurting him and apologizes. Frustrated Ved leaves. Next day, Ved continues his office routine with a change, gives a diamond ring to the transgender and he gets evicted from his workplace for his continuous mindless behaviors.
Ved comes back to Shimla and reveals he was jobless and wandering for six months. After a tussle with his father, Ved gains introspection from a reflection in the mirror, he realizes that to complete his own story, he needs to meet the old story-teller. The old story-teller criticizes Ved's irrationality and confronts him to complete his own story. This opens Ved's eyes. Ved narrates his life story to his family members. Moved by this, his father forgives him for leaving engineering and lets Ved pursue his life as he wishes.
Ved returns to Delhi and takes the diamond ring returned to him by the affectionate transgender. Tara, after finishing a business meeting at Oracle in Tokyo, heads for refreshment where she finds a note titled "Don Returns". Perplexed about Ved's presence, she moves around the office campus and Ved draws her attention with the "Don" personality from Corsica. The film goes into a flashback and shows scenes from Shimla of a free spirited-young Ved, a college going Ved and an adult Ved. The film returns to present day (first scene of the film) where Ved and Tara complete the process of putting up an elaborated skit on stage (in continuation of the opening scene of the film) a spectacle which depicts of their own life story.