"Red," said Ed. "Red again. Red again."
"That's 'O'," exclaimed Will. "I guess we've got him at last!"
"Now there's another red," Ed went on. "Now there's a blue. Then one more red. Ob, this seems to be easy!"
"That's 'K'!" cried Will. "O.K., don't you see? O. K. That means that he knows we're here!"
"Glory be!" shouted Ed. "The boys are all right or they wouldn't be signalling. I hope they've found Bert!"
Will signalled back "O.K.," and then the lads turned back up the rivulet, the idea being to cross over to the north side.
"I want to find out why the boys don't show themselves instead of signalling," Will explained. "There must be some good reason."
After a walk of half a mile upstream the boys found it possible to cross without wading, and then they turned down toward the mouth of the cavern where the lights had been seen.
As they did so, two figures detached themselves from a group of trees which stood not far to the east and followed stealthily along behind them.
If the lads could have heard the conversation carried on at that time between Cameron and Fenton, they would have proceeded on their way with less confidence.