The basic idea of this story is that a 10 year old boy named Conradin (who is terminally ill) is living with his cousin, Mrs. DeRopp. They hate each other. She is pretty harsh with him, always trying to make him unhappy.
Conradin has a pet hen that he loves and a pet ferret (they are both in a shed out in the garden) that he comes to worship as a god. He prays to it, among other things, to have bad things happen to Mrs. DeRopp.
Mrs. DeRopp eventually finds out about the pets and decides to get rid of them. When she does Sredni Vashtar the ferret kills her (seemingly in response to Conradin's prayers).
The story ends with Conradin happy because this has happened.
Hope this can help you...
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.