He turned immediately, and using the same precautions as before made good his retreat, and returned by way of the drawing-room window to the library.
All was silent there, and the empty room displayed no sign of its nocturnal visitors. Gimblet did not hesitate. He went straight to the clock and pulled open the door. The black interior was as empty and bare as when he had previously examined it, but he betrayed neither astonishment nor doubt as to his next action.
Stooping down he ran his hand over the painted wooden flooring. As he expected, his fingers encountered a small knob in one of the corners, and he had no sooner pressed it when the whole bottom of the case fell suddenly away beneath his touch. As he stretched down the hand that held the electric torch, the light fell upon an open trap-door and the topmost step of a narrow flight of stairs, which descended into the thickness of the wall.
Gimblet stepped into the case, and lowered himself quickly through the hole at the bottom.
The stairs proved to be but a short flight, ending in a low passage, which wound away through the wall of the ancient building. The detective felt little doubt that it led to another concealed opening in some distant part of the castle. But he had other things to think of for the moment.
"The clock—eleven—steps." The meaning of Lord Ashiel's dying words was, he thought, plain enough now.
Running up the stairs again, he descended more slowly, counting the treads as he went.
There were fifteen.
Gimblet bent down and held his torch so that the light fell bright upon the eleventh step.
It presented identically the same appearance as the rest, the rough-hewn stone dipping slightly in the middle as if many feet had trodden it in the course of the centuries which had elapsed since it was first placed there, but in every respect the worn surface resembled those of the steps above and below it, as far as Gimblet could see.