The question below consists of a set of labelled sentences. Out of the four options given, select the most logical order of the sentences to form a coherent paragraph.
P. It had been umpteen years since we had seen each other.
Q. One dull dark day in autumn, I was travelling on horseback through a dreary stretch of countryside.
R. This was the house of Roderick Usher, who had been my childhood pal.
S. At night fall, I came in sight of the house of Usher.