He seemed to be stirring up the moat with something which he held in his hand.

Then suddenly he hauled something in as a fisherman lands a fish--some large, round object which obscured the light as it was dragged through the open casement.
"Now!" cried Holmes.

"Now!" We were all upon our feet, staggering after him with our stiffened limbs, while he ran swiftly across the bridge and rang violently at the bell.

There was the rasping of bolts from the other side, and the amazed Ames stood in the entrance.

Holmes brushed him aside without a word and, followed by all of us, rushed into the room which had been occupied by the man whom we had been watching.
The oil lamp on the table represented the glow which we had seen from outside.