Theory:

     The river breeze was bracing, and yet a slight discomfort lingered in Bepin Babu’s mind.
 
     Around Hastings, Bepin Babu decided to roll up his trousers and take a look at his right knee.
 
     There was the mark of an old inch-long cut. It was impossible to tell when the injury had occurred. Had he never had a fall as a boy and cut his knee? He tried to recall such an incident, but couldn’t.
 
     Then Bepin Babu suddenly thought of Dinesh Mukerji. The man had said that Dinesh was in Ranchi at the same time. The best thing surely would be to ask him. He lived quite near — in Beninandan Street. What about going right now? But then, if he had really never been to Ranchi, what would Dinesh think if Bepin Babu asked for a confirmation? He would probably conclude Bepin Babu was going nuts. No; it would be ridiculous to ask him.
Explanation:
 
Bepin's car passed through the Ganga river as he requested his driver to do. Bepin wanted to travel that way as he thought the cool breeze and peaceful environment of the Ganga river would lessen his mental stress. But, though the river wind was refreshing, Bepin Babu' thoughts kept him a little uneasy and disturbed. Suddenly, the thought about the Hudroo incident mentioned by Ghose stuck in his mind. So, Bepin Babu rolled up his pants and examined his right knee as he passed through Hastings. Hastings is a part of the Kolkata district.
 
Bepin was shocked to see an old inch-long cut while examining his right knee. So, Parimal Ghose was right about this point too. Still, Bepin was unable to say exactly when the injury occurred. As far as he could remember, he had never fallen and hurt his knee as a kid. He tried to think about such an incident but unable to recollect such an incident.

Then Bepin Babu was reminded of Dinesh Mukerji. Dinesh was said to have been in Ranchi at the same time as Bepin, according to Parimal Ghose. So, rather than confusing himself, he felt it would be best to approach and ask Dinesh directly. Moreover, unlike Haridas, who was in Japan, Dinesh resided more closely to Bepin; he stayed in Beninandan Street. So Dinesh's house was not far away from Bepin's place.

Things on and about Ranchi confused Bepin. So, he decided to see Dinesh right away. But, he wondered how Dinesh would react if Bepin Babu asked for confirmation whether Bepin had been to Ranchi. Dinesh would indeed conclude that Bepin Babu was insane in such a situation.
 
Meaning of difficult words:
 
S.No
Words
Meaning
1.
ConfirmationA statement saying that something is true or accurate
2.
Going nutsGoing mad
3.
Indeed In reality
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.