Hello! You wanted to know what happens in Anita Desai's short story "A Devoted Son."
The short story starts out in a celebratory mood. Rakesh, Varma's son, is at the top of the first division list in the country: he has excelled in his exams, and the family is bursting with pride. Some accuse Varma of putting on airs, and some complain that pure ghee sweets should have been served at such an important occasion for celebrating Rakesh's accomplishments. All are envious that Varma's son has succeeded beyond the whole village's imagination and that this son is as filial as ever, despite his success. With a much lauded thesis, a scholarship, and a career at a prestigious hospital in the United States under his belt, Rakesh continues to be a faithful son. He bows down and touches his father's feet in great respect; he comes home to marry a local Indian girl of his mother's choosing.
Rakesh works in the local city hospital and rises up to the rank of director, before eventually leaving to start up his own clinic. He drives his parents in his new Ambassador to see his clinic, where the name plate on the door showcases all his many degrees and qualifications. Time soon sees his father retire from the kerosene dealer's depot and his mother suffer from a fatal illness. She dies, contented in the fact that her son ministers to her so tenderly during her illness. Everyone is amazed at this son of illiterate parents: he is equal parts medical wizard, filial son, quintessential family man, and neighbor-of-the-year.
Soon, we learn that all is not well with Varma. Having retired and lost his wife, he becomes listless and falls ill. He develops strange behaviors that exasperate his family. Eventually, everyone ignores him, except his son, Rakesh. Rakesh ministers tenderly to his father, takes him his tea, reads and discusses the news with him, and persuades his father to take the evening air in the garden. All this is extremely gratifying to the aged father, but Rakesh soon comes to irritate Varma by his almost arrogant assumption of authority over his father's diet. After a very trying illness, Rakesh decides that Varma is no longer to have fried foods or overly rich and sweet desserts. Varma is incredulous: how dare the son treat his father with such disrespect and deny him his favorite foods?
Soon, Varma feels completely subjugated by the medical tyrant. Rakesh has prescribed a diet of boiled foods for Varma, and the diet depresses Varma. He resorts to bribing his grandchildren to bring him sweets. When Rakesh discovers this, he accuses his old father of teaching bad habits to his children. With cholera, typhoid, and gastroenteritis in the city, Rakesh forbids his entire family from buying sweets at the local bazaar, and that includes his own aged father. Rakesh has assumed, almost overnight, the mantle of head of household, in what used to be Varma's domain. The only pleasure left to Rakesh is an occasional visit from old friends.
Varma complains to his friend, old Bhatia, that Rakesh is making his life miserable. Bhatia says that he cannot believe a son would deny a revered father his favorite foods, even in this evil age. Varma confesses that Rakesh does not allow him any butter or oil, and he cannot even have a piece of fried fish. Under this punishing diet, Varma eventually becomes a truly sickened old man. Now, on top of his strictly sparse diet, he also has to down the many pills Rakesh prescribes for him in order to combat his many ailments. Varma tells old Bhatia that this is the way great doctors treat their fathers and implies that Rakesh shows no gratitude for all that Varma has done for him. Varma begs Rakesh to just let him die.
Rakesh is incensed. He thinks his father the ungrateful one; after all, he is only doing what's best for his father. When Rakesh brings back a new bottle of yet another tonic for Varma, Varma sweeps the bottle out of his son's hand, and the bottle crashes to the floor. He will no longer tolerate his son's overbearing tyranny. The story closes with Varma once more begging to be let alone to die.
Hope this helps. Thanks for the question.