Angry River is about Sita, a girl who lives with her grandparents in a hut on an island. Her grandfather is a fisherman. One of the walls of their hut leans against a rock and the other three walls are made of mud. At the beginning of the story, Sita's grandmother is extremely ill and Sita's grandfather plans to take her grandmother to the hospital in town. He leaves in a boat with three of his goats and tells Sita that he will be back in a few days. He also warns her of the rain saying that the rain might cause a flood and that if the level of the water goes very high, she must climb the peepal tree on the island.
Soon, it begins to rain heavily. Sita goes outside and realizes that there is a flood that looks like a raging river. She sees a few things floating around in the water. She hurriedly packs some spices, fish, her grandmother's saree, and grandfather's hookah in a trunk. She then climbs up the peepal tree but she forgets her doll, Mumta. The flood soon reaches the level of the peepal tree and she almost gives up hope when she sees a boy in a boat trying to rescue her. The boy rescues her and she forgets about Mumta. Once the two are out of danger, the boy introduces himself as Krishan. They eat mangoes that were in the boat. Never before did Sita eat mangoes that were as sweet as the ones Krishan had offered. Sita later comes to know that her grandmother had died and she returns to the island with her grandfather to build a new house and continue life without her doll Mumta and her grandmother.
Meena Khorana in her study of Ruskin Bond's life and works cites Angry River as an example of his works' rootedness in the culture and traditions of India.