(a second draft of the story i posted last time. i've changed the ending for clarity.)

The young swordsman squinted out at the desert. “What do you think it is, Sir Isaac?” He drained the last of the canteen, then spit the lukewarm water over the edge of the parapet with a grimace.

Isaac was just coming up the stairwell, polishing his sword with a square of cloth. “Should have swallowed that. We’ll be on short rations until we take the oasis.” The knight glanced up at the sun, which was perhaps an hour from its slumber beyond the horizon. Squinting himself, he peered out at the glint of light atop the dune, perhaps a thousand paces outside the fortress wall.

“You see it? Looks like someone left a sword out there. I thought we gathered them all after yesterday’s battle.”

“Apparently not,” Isaac replied coolly. He regarded the younger soldier’s curved scabbard, and the ornate hilt emerging from it. “I see you’ve got yourself a nomad’s blade.”

Grinning, the soldier glanced down at his own sword admiringly. “It’ll hold me over until I get one like yours,” he said, nodding at the knight’s unsheathed blade. Even at this distance, he could see the sky in Isaac’s sword, a reflection creased with the nicks of battle.

“Indeed.” Isaac narrowed his eyes once again at the light in the desert. His left hand still polished the blade with an uneven rhythm, the cloth jumping back and forth across the steel.

“Sir Darren said he’d make me his squire if I made something of myself in the desert campaign,” the soldier said, his eyes distant, his mouth grinning still. “Not bad for a merchant’s kid, and a half-blood at that.” He turned and leaned against the parapet wall, looking back at the single tower of the fortress.

Isaac looked down at his sword for a moment, tilting it in the slowly fading light. Then, the rag moved once again, up and down the blade. “See that you do. This kingdom needs more low-born knights.”

“Amen,” the soldier agreed, turning back to the desert. He went to grab his empty canteen, then remembered. “Right.” With a shrug to himself, he threw Sir Isaac a glance. “I’ve heard that your mother was a nomad too, sir. Like mine.”

“Quite right.” Isaac stuffed the rag into his belt and sheathed his sword with a heavy clink, giving the young soldier a hard look. “Several have made an issue of it, and lived to regret it. I suggest you don’t.”

“Of course, sir. My apologies.” The young man lowered his head, surreptitiously looking back out at the dunes. As he did, the light flickered twice, and disappeared. The soldier raised an eyebrow. “Huh. What do you make of that?”

Isaac flicked his eyes at the missing glint and walked back toward the stairs. “The sun’s setting. It isn’t in the light anymore.”

“Of course, sir,” the soldier repeated. Something in his voice made Isaac pause, turn back to the swordsman. His eyes remained on the desert, averted from the knight. Sir Isaac shook his head and began to descend the stairs.

"My mother taught me the nomads' signaling code, sir."

Isaac stopped. His gaze remained fixed on the stairs, but his hand went slowly to the hilt of his sword. The swordman watched as the knight's fingers wrapped around and gripped the handle. Isaac said nothing, and looked out at the dunes.

The swordsman, with a sigh, drew a dagger from his belt. "You told them when the guard changes." Eyes on Isaac, the swordsman flipped the dagger at the watchman's bell at the corner of the parapet. The dagger took one slow turn and struck the bell, the clatter of its landing on the stone deck lost in the bell's single, reverberating toll.

Down the stairs, the sound of armored men approaching, fast. Isaac slipped his sword from its scabbard and returned to the top of the stairs. The last of the sunset echoed from the blade, bright as a signaling mirror. Hesitantly, the swordsman drew his nomad steel, raising it to guard.

"So, you want to make something of yourself," Isaac sneered, taking the first step forward. The armored boots reached the bottom of the stairs behind him. "You think I'm a traitor, don't you?"

The half-blood swordsman flexed his swordarm. "Not to the enemy."

Dark eyes seething, Isaac stopped halfway across the deck. More than ever, he looked like a nomad raider, scowling fiercely at the swordman and his plundered blade. The soldiers behind him topped the stairs.

"Your mother would be proud," the traitor Isaac spat, the moment before his head left his shoulders.