The day passed swiftly, in intense watchfulness on the part of the defenders, and in a waiting game on the part of the besiegers.  They kept up a desultory firing all afternoon.  Now and then a reckless grader running from post to post drew a volley from the Sioux; and likewise something that looked like an Indian would call forth shots from the defenses.  But there was no real fighting.

It developed that the Sioux were waiting for night.  A fiery arrow, speeding from a bow in the twilight, left a curve of sparks in the air, like a falling rocket.  It appeared to be a signal for demoniacal yells on all sides.  Rifle-shots ceased to come from the slopes.  As darkness fell gleams of little fires shot up from all around.  The Sioux were preparing to shoot volleys of burning arrows down into the camp.

Anderson hurried in to consult with Baxter.  “We’re surrounded,” he said, tersely.  “The redskins are goin’ to try burnin’ us out.  We’re in a mighty tight place.”

“What’s to be done?” asked Baxter.

Anderson shook his head.

On the instant there was a dull spat of an object striking the roof over their heads.  This sound was followed by a long, shrill yell.

“That was a burnin’ arrow,” declared Anderson.

The men, as of one accord, ran out through the engineers’ quarters to the open.  It was now dark.  Little fires dotted the hillsides.  A dull red speck, like an ember, showed over the roof, darkened, and disappeared.  Then a streak of fire shot out from the black slope and sped on clear over the camp.

“Sooner or later they’ll make a go of that,” muttered Anderson.

Neale heard the scout’s horse, that had been left there in the inclosure.

“Anderson, suppose I jump your horse.  It’s dark as pitch.  I could run through—­reach the troops.  I’ll take a chance.”

“I had that idee myself,” replied Anderson.  “But it seems to me if them troopers wasn’t havin’ hell they’d been here long ago.  I’m lookin’ for them every minnit.  They’ll come.  An’ we’ve got to fight fire now till they get here.”

“But there’s no fire yet,” said Baxter.

“There will be,” replied Anderson.  “But mebbe we can put it out as fast as they start it.  Plenty of water here.  An’ it’s dark.  What I’m afraid of is they’ll fire the tents out there, an’ then it ’ll be light as day.  We can’t risk climbin’ over the roofs.”

“Neale, go inside—­call the boys out,” said Baxter.

Neale had to feel his way through the rooms.  He called to his comrades, and then to the women to keep up their courage—­that surely the troops would soon return.

When he went out again the air appeared full of fiery streaks.  Shouts of the graders defiantly answered the yells of the savages.  Showers of sparks were dropping upon the camp.  The Sioux had ceased shooting their rifles for the present, and, judging from their yells, they had crawled down closer under the cover of night.