He left the mastiff where she had fallen and, as the darkness increased, drew closer to the mill.  Then he saw a man approaching and recognized Matlock Styles.  The Englishman entered the old mill, closing the door carefully behind him.

“More ghost work, I suppose,” murmured the detective, but he was mistaken, no such manifestations occurring.  Evidently they were to take place later.

Without making a sound he crawled up to a side door of the old mill.  It was unfastened, and pushing it open, he entered the lower floor of the building.  All was silent.

He waited and after awhile heard a step overhead and a low murmur of voices.  Then a man came down a narrow stairs, carrying a pole, a white sheet and a round, flat pan in which evidently something had been burnt.

“Looks like the ghost outfit,” thought Adam Adams, as he crouched down behind some empty boxes and bins.

The fellow was tall, broad-shouldered and powerful looking, and Adam Adams felt certain he was not Matlock Styles.  He wore a thin white bag over his head, with two holes for seeing purposes, and in one hand carried a flash lantern.

To the detective matters seemed to be growing tremendously interesting.

The man placed the things he carried in a closet partly filled with rubbish.  Then he flashed his light around carefully.  Adam Adams got down out of sight and placed his hand on the butt of his pistol.  He was resolved to take no more risks than were absolutely necessary.

Presently the light was lowered, and taking a peep Adam Adams saw the man kneeling down and tugging away at an iron ring in the floor.  Soon a trapdoor came up, and the man, taking up his lantern, disappeared from view, closing the trapdoor behind him.

The detective waited for several minutes and then stole forward in the utter darkness.  He had measured the distance perfectly and found the iron ring with ease.  He pulled upon it gently but firmly and raised the secret door several inches.

A look below showed nothing but darkness.  He strained his ears, and heard a faint noise at a distance but could not determine whether it was the flowing of the river over the stones or something else.

He got out his pistol and examined it with care, to make certain that it was ready for use.  Then, with a quick motion, he threw up the trapdoor, dropped below, and closed the opening above him.

He felt as does a lion tamer stepping into a cage of beasts new to him.  He realized that he was on the verge of some important discovery, but that this investigation might cost him his life.

He was on a narrow staircase.  There were but ten steps and then he found himself between two stone walls with the roof just above his head.  Not caring to take another drop into the unknown, he advanced slowly, taking no step until he was sure of it.

Presently he came to a turn and then another.  He could now see a light shining ahead, coming from under a heavy wooden door.  The barrier was tightly closed.  He tried it softly, to find it fastened on the other side.