o not know! The risk is that you may find you have crossed the
barrier in vain. There is yet the gulf. Go quickly! I hear a step--some
one comes! He is almost here!"

"But, dearest one--!" I protested, as she vanished.

There came a sound of quick steps behind me, and an angry voice muttered
the fierce oath, "_Carrajo!_"

A man reared in the wilderness acquires the instinct of the wild
creatures to act first and consider afterwards. I leaped away from that
angry voice before the last syllable of the oath hissed out. Even at
that I felt the prick of a sword point beneath my shoulder as I bounded
away. The owner of the voice had thrust--and thrust to kill. As my feet
touched earth again I had out my pistol; as I spun about, I set the
hair-trigger. The glint of a steel blade directed my gaze on the instant
to the dim figure crouching to spring after me.

"Halt, senor assassin!" I commanded. "Take a step, and I shoot you down
like a dog!"

"_Peste!_" he cried, lowering his sword point. "It is the _Americano_
physician."

"And you are Medina!" I muttered between my hard-set teeth--"Medina, the
aide-de-camp and bravo of Salcedo,--Medina the assassin."

"_Peste!_" he repeated. "It is a lie."

"You had better pray than swear," I warned him. "The trigger of my
pistol is set. The slightest touch of my finger, and you go straight to
hell."

"_Santisima Virgen!_" he protested, a trace of concern beneath the
continued anger of his tone. "You do not comprehend."

"I comprehend that you, an officer in the service of His Most Catholic
Majesty, sought to stab me in the back without warning. It was vile--it
was cowardly! Can you name a single reason why I should not shoot you?"

"You do not comprehend!" he insisted. "I mistook you for one of those
whom I have warned."

"Mistook me?" I repeated, catching at the chance for an explanation. It
is not pleasant to think of a gentleman and officer turned assassin.

"Yes," he answered. "I have made this my privilege. Any man in Chihuahua
who wishes to serenade Senorita Vallois has my pledge that I will kill
him."

"I am in Chihuahua, and I have serenaded Senorita Vallois," I replied.

"But you did not know of my pledge. I will spare you this time."

"_Muchas gracias_, senor. Yet it seems to me it is a question of my
sparing you."

"In that case, Senor Robinson might do well to consider that His
Excellency, the Governor-General, would gladly welcome an excuse to
garrotte a c