turned his eyes in this quarter and that, Rob failed to see
anything that looked at all suspicious. Still that peculiar odor
continued to strike his sense of smell, stronger than before, if
anything.

"Must be something burning, fellows!" announced Tubby, as he held a hand
up so that he could close his nose with thumb and finger against the
offensive odor.

The guide had meanwhile thrown himself down at the brink of the stream
and proceeded to drink his fill. Evidently he had no fear concerning the
quality of the water. Typhoid germs were unknown to his lexicon; and so
long as water looked fairly clear it suited him.

He was getting on his feet again as Tubby made that last remark. His
horse had been pulling more violently than ever at the rein, and the
Belgian started to say something uncomplimentary to the animal in
Flemish.

Rob had stopped examining the shore upon which they were standing. He
turned his gaze across the stream to the opposite bank, for his scout
training told him that since the breeze came from that quarter he would
be apt to learn the cause of the odor, so like burnt powder, if he
followed it up.

The others heard Rob give a half suppressed shout, as though he had made
a sudden and startling discovery.

"Oh! what is it?" cried Tubby, straining to keep his horse from trying
to start up the ascent again.

"Across the river, over there under the arch of the bridge, don't you
see that little curl of blue-white rising?" exclaimed Rob. "Watch it and
you'll find that it is creeping along over the ground. Come, we've got
to get up out of this in a hurry! Turn your horses, and let them help
to drag you up! Quick, everybody; not a second to lose, I tell you!"

Tubby no longer tried to hold his horse back; on the contrary, he even
urged the animal to climb the grade in frantic haste. He did not know
what it all meant, but Rob acted as though there must be some terrible
danger threatening them; and Tubby was no fool.

With cries and shouts they urged the animals to ascend. Several times a
horse would slip, and come near falling headlong backward; then it was
the one who held the reins found it necessary to encourage the
struggling beast with word and act, so that the horse might regain his
footing.

Tubby, chancing to glimpse Rob's face about the time they drew near the
top was horrified to see how very white it seemed. Then more than ever
did he realize that it must be something dreadful that had