All right, here's my story. It takes place just after Eliwoods' return to the Dread Isle and Just before Chapter 30, when they battle Limstelle. The Black fang has sent a forward assassin to eliminate Jaffar before they attack Eliwoods' forced in their sleep

DISCLAIMER: I do not own Fire Emblem, Intelligent Systems, or anything else in this story for that matter.

The assassin moved without a sound, his footsteps making no noise, his movements nearly invisible in the shadows of the tents. Jaffar saw him anyway. Silently drawing a Killing Edge from his cloak, Jaffar rolled onto his side, seemingly still asleep. It had been forever since he had truly slept; now he had learned to rest his body and mind, but to stay alert. Too many young thieves envied his position in the Black Fang for him to indulge in true rest. He braced his legs against the tent pole, waiting for the assassin to enter. Jaffar counted down the time, 5...4...3...2...1... snap! So predictable. Jaffar kicked out the tent pole, the black tarp falling upon the two killers. The former Angel of Death pounced, taking the would-be assassin down in a heartbeat. In a single, fluid motion, Jaffar stabbed the Killing Edge soundlessly into his assailant's chest. To the thief's credit, he didn't scream. Jaffar was up and running in the blink of an eye, racing towards Eliwood's tent as fast as his legs would carry him.

"Lord Eliwood! I need discuss something with you," he then gestured at the tactician, "You as well, we may need you too."
"Very well, Jaffar, what is it? You look pale."
"Lord Eliwood, we are under siege, or will be soon." Jaffar told him grimly.
"What? By who?" inquired the young lord, his face now worried.
"The Black Fang, of course. They just attempted to assassinate me. I know their tactics, they feared me and what I know, so they would kill me first, then destroy the camp in a destructive ambush. Even now, I imagine troops are silently placing themselves in our midst." He replied, his voice emotionless as always.
"Lord Eliwood? Jaffar? I do believe I have a plan" came the tacticians' feminine voice from the back of the tent. She then laid out her devious plan.

Silently, Jaffar roused the whole of Pherae's forces, if the enemy didn't know they were aware of an attack, the ambush could be turned back on them. Their brilliant tactician had imparted this advice, as well as Jaffar's role.
After rousing the camp, Jaffar returned to his own tent, quickly switching his clothes with that of the dead thief, covering the hole in his leather armor with his cloak. It was simple for the Assassin to follow the thief's trail back to the enemy camp. He strode into what was obviously the leaders tent, pausing to note that a majority of the forces had left for Eliwood's camp.
The Morph stared up at Jaffar with eerily glowing golden eyes and asked, "Is it done?" in a cold, emotionless voice. Jaffars' only reply was a sudden pounce, burying a Killing Edge deep within the Morph's chest before it could make a sound. With his right hand, he drew a second blade. In a single spinning motion, he freed the first blade from the dead morph and planted the second into one of the morph's two guards' forehead. The second bodyguard rushed him, and Jaffar dropped swiftly into a crouch, driving the dagger home.

Back at the camp, Pent and Canas were lying in wait for a signal to attack, the tactician said they would recognize it, but Canas was not so sure. However, they soon heard the voice of the Lord Eliwood cry out, " ATTAAAACK!!!!!"
"Canas, I do believe it would be safe to consider that the signal?"
"Agreed"
Their tent erupted in a huge explosion of magical power as the spells Nosferatu and Elfire burst forth simultaneously, obliterating a squad of unfortunate mercenaries.

Arrows and magic whizzed over Karel's head as he struggled to focus on his own enemy. After slaying him, Karel took a moment to survey the overall progress of the battle. Eliwood's forces were hard pressed but holding their own in the battle. Karel had only time for a quick glance before launching back into the fray. He spotted a pair of brigands teaming up on Hawkeye, which Karel was sure he could handle. However, Hawkeye did not see the sniper lurking in the bushes behind him. Karel moved swiftly to close the distance between himself and the archer, finally closing into range of his attack. In the blink of an eye, Karel had moved a space of three meters and was on the sniper, hacking away with his Wo Dao.

Jaffar burst out the front of the tent, moving swiftly but silently to place himself behind a sword-wielding sentry, simultaneously covering his victims' mouth with one hand, and slitting his throat with the other. Unfortunately, Jaffar had failed to notice the Cavalier behind him, who shouted for help at the top of his lungs. His cries quickly turned into a sickening gurgle as Jaffar plunged his wickedly curved Killing Edges into his lung. His scream did not go unheard though, and Jaffar was soon faced with two morph assassins, and ten brigands, all armed to the teeth.
Moments later, Jaffar walked away from the thirteen bloodied bodies, cool and composed as ever.

"The attack has subsided, Lord Eliwood, Jaffar must have been successful." reported a jovial Serra, a wide grin on her face, Erk resisted the urge to vomit.
"Very good, Serra, has Jaffar returned yet?" Eliwood asked.
"Jaffar left?" Serra replied, seeming confused, "I haven't seen him."
"Uh-oh, I'll take that for a no." Eliwood murmured, growing worried. Please guide him back, St. Elmine. Eliwood prayed to himself, closing his eyes.

Crouching behind a tree until he saw the coast was clear; Jaffar heard a twig snap behind him. He whirled to find a warrior standing behind him, axe raised. Inwardly cursing himself for letting the barbarian get so close, Jaffar nimbly dove to the side, avoiding the axe swipe and allowing himself to side step around his opponent and drive a curved dagger in his back. "Dammit, Jaffar, you're slipping," he whispered to himself. Silent as a shadow, he began moving back toward Eliwood's tent. Much earlier this time, Jaffar's honed instincts detected the clumsy attempt at stealth that the enemy was making and was puzzled for a moment, then it dawned on him. This was the army retreating from their failed ambush. Jaffar was now effectively trapped between a rock and a hard place.