"Thank you, sir," smiled Shelton. "That material way you have of supplementing a prayer is not a bad thought. I may count upon your silence about what I have disclosed--may I?" Mr. Lawrence placed his fingers on his lips with a nod and smile. "All right, I'll rely upon you," said the disguised detective, and with a brief "good-day, sir," he went buoyantly away on the secret mission that meant detection and ruin to Messrs. Pratt and Colville. The banker returned to his counting-room with renewed hope and vigor. The impenetrable darkness that had hovered over Lily's disappearance so long seemed to be lifting at last and a gleam of light shone through the little rift in the clouds. CHAPTER XXII. Mr. Shelton spoke truly when he said to Mr. Lawrence that he would shadow Harold Colville like a bloodhound. By day and by night, on foot or on horseback, in various disguises, he kept himself on the track of the fine gentleman. For several weeks he kept up this close espionage, but at the end of that time he seemed no nearer his object than when it was first begun. Mr. Colville's comings and goings seemed to be quite the same with those of other gentlemen of his means and position. He frequented theaters and gaming-houses; he was a welcome and much sought-for partner in ball-rooms, and was smiled upon by scheming mothers with marriageable daughters. Thus far Mr. Shelton had seen nothing on which to seize as a possible clew to Mr. Colville's mysterious presence in Mr. Lawrence's house the night of Lily's appearance. Mr. Shelton had made one discovery, however, though he did not begin to attach much importance to it. It was that Doctor Pratt and Harold Colville were acquainted with each other, and, moreover, that they sometimes "hunted in couples." 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.