Drummond did not seem to be suspicious; his pose was careless, and Thirlwell imagined the lad was enjoying his triumph.

Both thought they were alone and they stood on a ledge that ran out into deep water.
Then Stormont clutched the stone and Thirlwell sprang to his feet.

The fellow's caution had given way; mocked and cheated by the lad he meant to use, he had suddenly become primitive in his disappointed greed and rage.

It looked as if Drummond did not know his danger; but as Thirlwell ran forward Stormont lifted the stone and the lad leaped upon him like a wild cat.
Thirlwell stopped.

For the moment he did not see how he could interfere without doing harm, and thought Drummond did not need his help.