Who is Yashwan Singh from Song of Kali and what is their importance?

Yashwan Singh is an inspector with the Calcutta Metropolitan Police, Singh, a tall, bearded, turbaned Sikh, receives military training in England. This gives him the accent of Sandhurst rather than Oxford. His tailored tan suit is almost a uniform. A steel bracelet and concealed miniature dagger remind him constantly of his faith. Singh first visits narrator Robert C. "Bobby" Luczak at Calcutta's Oberoi Hotel to ask if he knows the whereabouts of the supposedly-deceased poet M. Das. Das' file, begun in 1969, is still open and Das' influential friends would like closure.