Naina Talwar (Deepika Padukone) is a shy and nerdy medical student. She studies constantly and always tops her classes, but she feels like an outcast due to her introverted nature. An encounter with an old classmate, Aditi Mehra (Kalki Koechlin), makes her realize that she wants more from life than high marks. Thus, she makes an impulsive decision to follow Aditi on a hiking trip into the Himalayas, up to Manali without informing anyone. During the hike, she renews her friendship with other former classmates, Kabir “Bunny” Thapar (Ranbir Kapoor) and Avinash “Avi” Yog (Aditya Roy Kapur). Kabir is a handsome charmer whose dream is to wander and discover the world. He does not plan to marry or settle down. He lives with his supporting father whom he loves very much, and his step-mother. During their trip, seeing Aditi’s silent reactions to Avi’s constant flirting with other girls, Kabir and Naina realize that she is secretly in love with Avi, but do not bring the matter to surface.
In the course of the mountain trek, Kabir and Naina come closer to each other. Kabir teaches Naina to laugh, to play, and more importantly, to love. At the end of the trip, she is close to telling him how she feels but is interrupted by Avi. He accidentally finds a letter accepting Kabir into a graduate school in journalism, at Northwestern University in Chicago. Kabir explains that the trip is his last hometown adventure before he leaves. He is sad to leave his friends but happy to start a career that will lead to travelling, which he dreams of, and thus wanted to bring them along to Manali to give them a surprise. Naina realises that love and marriage have no part in Kabir’s plans and remains silent about her feelings but is happy for him as he is following his passion.