They are Piyali Roy (Piya), a Bengali-American cytologists from Seattle who cannot even speak her mother tongue, and Kanai Dutt, a prosperous and proud owner of a translation business in New Delhi. The narrative space is taken up by them and a handful of other characters, each on a personal quest through life. Piya is drawn by the tidal water; she has come to study the Irrawaddy dolphin, Orcaella Brevirostris, a rare river dolphin that can negotiate the mix of fresh and salt water. She is trying to unravel the mystery of this marine mammal that lives in the tidal pools, where they travel. Kanai, on the other hand, has been summoned to the land by his aunt, Nilima Bose (Mashima), a renowned a social worker who runs a trust named Badabon Trust that supports the rights of the poor and the underprivileged and offers manifold services like medical, paralegal and agricultural to a population of several thousands in Lusibari, the most southerly of the inhabited islands of the tide country. He comes to Lusibari on account of a discovered notebook – a diary of sorts written by his late uncle and addressed to him. He uses this notebook to another mystery, that of his uncle's death. Linking the two narrative strands is Fokir, an illiterate fisherman who knows the watery labyrinths of the Sundarbans better than anyone. The first section of story is held in two different places, one is the notebook that reading by Kanai, and the other is Piya who searches for a dolphin species in the Ganges with Fokir and his son Tutul. The entire part of the story also divided into two, One is the notebook that explains the past that held in Lusibari, Canning, Morichjhapi, Other is the present that held with Kanai, Piya, and Fokir that make up the narrative structure of the novel, are unfolded in a braided manner in alternate chapters, the former shedding light on, and containing the seed of, the latter.