The story revolves around two people who, despite being childhood acquaintances and their families being old friends, lead drastically different lives. Two decades after Kaushik's family stays with Hema's as houseguests, they meet again by chance, just days before they are to enter into completely different phases of their lives, and they discover a strong connection with one another. The entire story of Hema and Kaushik is divided into three parts.
"Once in a Lifetime"
This section deals mostly with their childhood and is written in a first person address from Hema to Kaushik. It tells the story of two families who were close to each other because of shared culture and the common experience of adapting to a new culture, but who are beginning to drift apart due to reasons which become evident as the story progresses.
This part is from Kaushik's point of view and tells about his life after his mother's death as he deals with unwanted change and navigates complicated relationships with his recently remarried father, stepmother, and two young stepsisters—a situation that will ultimately influence Kaushik to lead the life of a wanderer.
The last part is related by an omniscient narrator as Hema and Kaushik meet by chance in Italy after two long decades. Hema, now a college professor, is tormented about her previous affair with a married man and plans to settle down by marrying Navin, someone she barely knows. Kaushik, a world traveling, successful photojournalist, is preparing to accept a desk job in Hong Kong. In spite of all that, they find their deep connection irresistible. They coincidentally reunite in Rome and relive their younger years together, exploring Italy together. Before leaving for a Christmas vacation, Kaushik asks Hema to leave Navin and come and live with him in Hong Kong. He tells her to brood about it while she is in Calcutta.
Kaushik ultimately dies vacationing in Khao Lak when the 2004 tsunami occurs, never giving Hema a choice regarding their future together.