A sickly ten-year-old boy lives a miserable life in the house of his domineering cousin guardian. However, He would not live another 5 years of his life because he is sick. He creates a fantasy religious cult in a garden shed, where his idols are a hen and a ferret. He is a lonely and imaginative young boy. One day he bought a polecat-ferret and named it Sredni Vashtar. Conradin lived with Mrs De Ropp, his guardian. She is the one who took care of Conradin and responsible to serve shelter, food and clothes for conradin.
Although they lived together, Mrs De Ropp dislikes Conradin. She never shows her concern toward Conradin. In the story, Conradin keeps two animals in backyard shed which is a hen and a ferret. But, Mrs. De Ropp discovers the hen and told to Conradin that she has sold the hen to the butcher. When his guardian gets rids rid of his hen, he prays to the ferret for revenge. Then, Conradin turn his devotion to the Sredni Vashtar, a great ferret. It gives happiness to Conradin although he is sick. Sredni Vashtar is like a god for Conradin.
One day, Mrs. De Ropp realized that Conradin was keeping something else from her in the shed where Sredni Vashtar stayed. She goes the shed again. At last she finds Sredni Vashtar while Conradin prays to his god for the safety of his ferret. She went there to check it but she was been bitten in the throat by the ferret and died. Sredni Vashtar bite Mrs. De Ropp. The maid went to the shed and shocked. She screamed out loud as she discovers the dead body of Mrs. De Ropp while Conradin enjoys toast in the kitchen.
One morning, a boy called Nicholas doesn't want to eat his breakfast, and puts a frog in his bowl.His distant aunt gives out to him for this, and Nicholas's two cousins and younger brother are taken to the seaside at Jagbourough, while he has to remain at home as a punishment.
When the other children have left, Nicholas's distant aunt goes to work in the garden...