No sooner had he done so than he fell to the ground in a paroxysm of fear.
There, on his knees, motionless as a statue, and his dark face upturned, was the captain, staring at a misty blue light which seemed growing out of the side of the room.
Jem uttered a groan of dismay and horror as there slipped, or rather floated into the room the dreadful figure which he had seen at the oriel window.
It was the White Nun!
Slowly, and with a floating, gliding motion, the figure advanced.
Then it seemed to see them, for it moved its skull slightly in the direction of the men and stopped.
The captain, shaking off the horrible influence of dread, sprang to his feet.
He was about to advance to the horrid thing, but the blue light suddenly disappeared, the figure glided out of the stream of light flowing from the lantern, and all the captain saw was the fiery eyes and the dull gleam of the white, ghostly drapery.
"Ghost or no ghost," he hissed, "you shall not escape me!" and he sprang forward.
But before he could clutch the apparition it drew back with a gliding motion, and seemed to vanish through the wall.