The Temporal Knights

The first victims died on the fourteenth of June and before the month was out every human female, young boy and non-virile male was dead. Five billion people in all. In the wake of the tragedy came unbridled grief, disease and chaos…and finally Martial Law. Extinction was staring Mankind in the face. It took over a year to stabilize what was left of society, and then another full year before the first test tube baby girl was born. The entire world rejoiced! The Laws of Nature bent to the brilliance of the human mind. Mankind, that bizarre species of primate, had somehow managed to cheat death and endure…and then the aliens fell upon the planet in force.
Countless hoards of enemy soldiers poured down from the heavens. The invaders attacked and killed without hesitation, but they also died by the millions. The remaining human beings fought back desperately, but the enemy came in endless waves, relentlessly killing and destroying everything that was human. For five long years the battle raged on, until once again humanity was threatened with extinction. All appeared to be lost. Less than a thousand human beings lingered on earth, when a strange and bizarre solution presented itself. Discovered deep within the alien technology was the key to life, the key to time and the key to victory. The last of Mankind would move back through the ages to the year 893, to England, during the reign of King Alfred the Great. There, they would drag the dark ages into the light, speed up the process of enlightenment, and prepare Mankind for the coming battle. With luck, they would truly be ready when the alien invaders finally came again.
Those still alive would risk everything and cross over; it was that, or oblivion.
"We're like Twain's Yankee," Major Thane commented.
"Who?"
"You know, Twain's Yankee, 'The Connecticut Yankee in King Arthur's Court.' If we succeed in going back, our situation will be very similar." Thane explained.
Colonel Lemay grunted. "Yes, but this time we'll be bringing along machine guns and hand grenades."
"And don't forget the flamethrowers," Moore added with a laugh.