It seemed an age before the door was sufficiently open to allow him to wriggle through. He waited again; then moved slowly and warily forward, to find within a few paces that his foot was arrested by another step. He had come to a staircase. This time the flight wound round and round, and as he rose higher a glint of moonlight fell through a narrow slit in the right-hand wall; he must be on a winding stair within the tower. He left the dim light behind and came again into inky blackness; then, at another turn, another slit gave entrance to the pale beam. At last, after mounting until it seemed that his winding course would never end, he came into open air and full moonlight; he was on the roof of the tower. Before stepping out from the shelter of the stairway he glanced eagerly to right and left. The roof was vacant. It was hexagonal in shape. He wondered whether it was overlooked by other towers. Dropping on his knees, he crawled under cover of the wall that intercepted the moonlight, and made his way thus to the parapet. With relief he saw that the other towers were no higher, but apparently indeed a few feet lower. Completing the circuit of the roof, he came to another stairway immediately opposite the one he had just left. He entered cautiously, and found that this also was a winding stair, differing from the other only in the fact that there were no patches of light from slits in the wall. He went down step by step, quietly, until at a turn he was brought to a sudden pause by the sight of a small lamp burning in a niche opposite a heavily-barred door. For a minute he stood still; then stepped silently down until he came to the door. He listened; he ventured to place his ear against the wood: there was no sound. Waiting for a brief space, he hovered between advancing and retiring; then, with quickening breath, he moved on past the door until he came to the foot of the staircase.