Gangu is a Brahmin, a Hindu from the very highest cast. Despite his exalted social position, he is illiterate and uncultivated and works as a servant for the story's narrator. But Gangu retains something of his Brahmin pride and doesn't kowtow to his master like all the other servants.
One day, Gangu approaches his master and asks to be relieved of his duties. He's going to marry Gomti, a woman with a notorious reputation. The narrator is aghast; he simply cannot believe that Gangu would actually get married to someone so heartily despised among polite society.
Gomti's appalling reputation is based on the fact that she's been married three times previously and, in each case, left her husband after a very short time. In traditional Indian society, such behavior among women is frowned upon, and so Gomti has become something of a social pariah.
But Gangu's willing to give her another chance. He seems to pity her, believing as he does that she was driven out by her three previous husbands, who did not show her any love. He's heard all the bad stories about her, but he's adamant that they're all lies; people have been maligning her for no good reason at all.
Gangu acknowledges that Gomti appears to suffer from some kind of sickness. Sometimes she's possessed by a spirit, starts talking nonsense, and falls unconscious. That Gangu should want to marry a woman so afflicted reinforces the sense that he's motivated more than anything else by pity.