Then like a zigzag of lightning came the change.

Amory sat bolt upright, frozen cold in his chair.

Tom was looking at him with his mouth drooping, eyes fixed.
"God help us!" Amory cried.
"Oh, my heavens!" shouted Tom, "look behind!" Quick as a flash Amory whirled around.

He saw nothing but the dark window-pane.

"It's gone now," came Tom's voice after a second in a still terror.