Theory:

     And he knew how ruthless Dinesh’s sarcasm could be.
 
     Sipping a cold drink in his air-conditioned living room, Bepin Babu felt at ease again. Such a nuisance! Just because they have nothing else to do, they go about getting into other people’s hair.
 
     After dinner, snuggling in bed with one of the new thrillers, Bepin Babu forgot all about the man in New Market.
 
     Next day, in the office, Bepin Babu noticed that with every passing hour, the previous day’s encounter was occupying more and more of his mind. If the man knew so much about Bepin Babu, how could he make such a mistake about the Ranchi trip?
Explanation:
 
As it seemed to be a mere stupid idea for Bepin to ask Dinesh about the Ranchi trip, he did not want to do that. After all, Dinesh was not his well-wisher but an annoying person who bullied Bepin often. And, he was well aware of Dinesh's harsh sarcasm. But still, Bepin's thoughts and confusion on Parimal's talk made him lose his peace of mind.
 
Bepin Babu reached home after some time. He felt at rest, sipping a refreshing drink in his air-conditioned living room. He felt more peaceful in his air-conditioned room at home than near river Ganga. It must be that Bepin felt safe and protected from unwanted thoughts and confusion at his home. He was relaxed, being with greater peace of mind. Still, it didn't stay longer.
 
After some time, Bepin started to think about the book shop incident again. He was irritated with such an incident. Bepin couldn't forget Parimal's talk.
 
Bepin became annoyed when he remembered Dinesh. He felt people like Dinesh were annoying others as they have nothing else to do. After dinner, Bepin Babu forgot about Parimal Ghose, whom he met in New Market and got himself occupied with one of the new thrillers. A diversion from his restless thought made Bepin relax for a while, and he slept peacefully after some time.
 
As usual, Bepin went to his office the next day, but he looked stressed. Bepin Babu then realised that the previous day's incident took more of his attention with each passing hour. Bepin's only confusion was how the man (Parimal Ghose) could have made such a mistake regarding the Ranchi trip if he knew so much about Bepin Babu? He couldn't stop thinking about Ghose because all the details given by Ghose were true except for the Ranchi trip.
 
Meaning of difficult words:
 
S.No
Words
Meaning
1.
Ruthless Making other people suffer without showing pity on them
2.
Snuggling  To move yourself into a warm, comfortable position
3.
Sarcasm Use of words to mock someone
4.
AnnoyanceSomething that makes you angry
Reference:
National Council of Educational Research and Training (2008). Honeydew. Bepin Choudhury’s Lapse of Memory- Satyajit Ray (pp. 59-69). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.