That is to say, the worthy physician occasionally stopped his carriage on meeting Colville, whereupon the latter would spring in and accompany the doctor on his round of visits, seeming deeply interested in the conversation they pursued together.
Mr. Shelton was puzzled to decide whether there was any collusion between the gay man of fashion and the busy physician, or whether it was only one of those odd friendships that are sometimes observed to exist between persons of totally different temperaments and pursuits. Sometimes he was inclined to believe it was only the latter.
But he noticed a fact at last that struck him as rather peculiar. Following the pair closely on his stout, black horse, he had seen that Colville always remained in the carriage while the physician went into the houses to pay his visits to the sick.
On this occasion, which struck him so forcibly, they drove quite out upon the outskirts of the city, and stopped before a house standing almost a half mile distant from any other.
This house, the detective observed, had a gloomy and forbidding aspect, being closely shuttered and surrounded by a very high stone wall.
Here Dr. Pratt descended and fastened his horse. Mr. Colville also sprang out, and they entered with a familiar air, the heavy gate closing and shutting them in.
"Now, that is rather strange," thought the detective as he walked his horse slowly past the deserted-looking place.
"What business has Colville in there? I can imagine that Pratt may have a patient inside those gloomy walls; but what the deuce can Colville have to do with it? I am almost positive that I heard shrieks issuing thence when they went in at the gate. I wonder can it be a private asylum for the insane?"
He spurred his horse ahead and rode on for some distance, then paused, and remained as erect and still as a statue while he watched and waited for the pair of confederates to come forth. But at least an hour elapsed before they emerged, and pursued the devious tenor of their guilty way.
"Now, upon my word," thought the wary spy, "Doctor Pratt must have a very interesting case inside of those gloomy, prison-like walls. I have a mind to stop somewhere in the neighborhood and inquire about the inhabitants thereof."