“Now I know you, Mexico Sam!” muttered Littlefield to himself.  “It was you who shook your rattles in that gentle epistle.”

Mexico Sam did not leave things long in doubt.  He had a nice eye in all matters relating to firearms, so when he was within good rifle range, but outside of danger from No. 8 shot, he threw up his Winchester and opened fire upon the occupants of the buckboard.

The first shot cracked the back of the seat within the two-inch space between the shoulders of Littlefield and Miss Derwent.  The next went through the dashboard and Littlefield’s trouser leg.

The district attorney hustled Nancy out of the buck-board to the ground.  She was a little pale, but asked no questions.  She had the frontier instinct that accepts conditions in an emergency without superfluous argument.  They kept their guns in hand, and Littlefield hastily gathered some handfuls of cartridges from the pasteboard box on the seat and crowded them into his pockets.

“Keep behind the horses, Nan,” he commanded.  “That fellow is a ruffian I sent to prison once.  He’s trying to get even.  He knows our shot won’t hurt him at that distance.”

“All right, Bob,” said Nancy steadily.  “I’m not afraid.  But you come close, too.  Whoa, Bess; stand still, now!”

She stroked Bess’s mane.  Littlefield stood with his gun ready, praying that the desperado would come within range.

But Mexico Sam was playing his vendetta along safe lines.  He was a bird of different feather from the plover.  His accurate eye drew an imaginary line of circumference around the area of danger from bird-shot, and upon this line lie rode.  His horse wheeled to the right, and as his victims rounded to the safe side of their equine breast-work he sent a ball through the district attorney’s hat.  Once he miscalculated in making a detour, and over-stepped his margin.  Littlefield’s gun flashed, and Mexico Sam ducked his head to the harmless patter of the shot.  A few of them stung his horse, which pranced promptly back to the safety line.

The desperado fired again.  A little cry came from Nancy Derwent.  Littlefield whirled, with blazing eyes, and saw the blood trickling down her cheek.

“I’m not hurt, Bob—­only a splinter struck me.  I think he hit one of the wheel-spokes.”

“Lord!” groaned Littlefield.  “If I only had a charge of buckshot!”

The ruffian got his horse still, and took careful aim.  Fly gave a snort and fell in the harness, struck in the neck.  Bess, now disabused of the idea that plover were being fired at, broke her traces and galloped wildly away.  Mexican Sam sent a ball neatly through the fulness of Nancy Derwent’s shooting jacket.

“Lie down—­lie down!” snapped Littlefield.  “Close to the horse—­flat on the ground—­so.”  He almost threw her upon the grass against the back of the recumbent Fly.  Oddly enough, at that moment the words of the Mexican girl returned to his mind: