Note: 343GS was not made invulnerable merely for plot reasons. For example, Captain Keyes was not invulnerable while he was an important plot element. You could kill him on the Pillar of Autumn, only that killing him would alert all human crew to kill you.
Now, Chapter 4
Deep in space, a 700 meter long Covenant cruiser with dark gray armor and a gleaming shield flew through space. The pilot was 343 Guilty Spark and he was thinking about the next step in his plans Where next? A Covenant planet? He checked for all the nearest Covenant planets. The nearest were all heavily fortified, and attacking them, or even trying to pass them would be fatal. Maybe some of the other Halos, the other monitors would surely help me-
A loud voice on the comm systems interrupted his thoughts.
"Vessel 4210, what are you doing? You are not permitted to enter this restricted area! You are out of you assigned sector! Identify yourself at once!" the loud voice said.
A blue holo-panel appeared from a projection device on the floor and on it was the face of a gold commander elite. The elite stared at the Monitor for a few seconds, rather shocked by what was piloting the cruiser.
"What the hell are you?! The registered commander of this ship is…" There was a short pause as the elite looked down at a display panel. "Salgosh is the commander of this ship! You are in violation of Covenant Protocol 529, which states that all commanders must be registered to pilot a ship! Disable your weapons and power down your engines at once!" The commander elite yelled.
"This is my ship." Replied the calm Monitor.
"This is your last warning! If you do not comply, you will be boarded immediately. This is your last warning!" the elite said.
With a quick thought, 343 turned off the comm systems in his ship. Ha, boarding action. With that, he activated the automated plasma cannons of the ship. To his surprise, the cannons did not fire. After a few seconds it struck him that the automated cannons would not fire at other Covvie ships. He modified the autocannon program so that it would do the opposite. The cannons opened fire on several approaching dropships.
He looked at what was coming at him. There were 3 destroyers, about 500 meters long and arrow shaped with four autoguns scattered around the ship and a main plasma cannon at the tip of the arrow. There were also about a dozen fighters about 20 meters long and shaped much like a Banshee, with a fuel rod cannon mounted just under the cockpit. There was one large cruiser, about 800 meters long and shaped like a tube, with two wing like structures that each held an anti-matter missile launcher. The cruiser was deploying several "U" shaped 40 meter dropships, with the bridge and guns at the curve of the 'U". All of them had the familiar purple Covenant armor and every ship had an energy shield around itself, except for the fighters.
A dropship flew to one of the docking bays of the underside of the ship and attached itself on. 343 quickly turned on vid display of the docking bay. Inside, there were some common blue elites and two major jackals with orange shields trying to open the metal door that lead to the inside the ship. The Monitor activated the methane gas vents in the docking bay that was used for grunts returning to the ship. The gas hissed into to the bay, and in about 15 seconds, the elites began gasping for air. Realizing something was wrong, the rushed into back into dropship, motioning for the jackals to follow. In a few minutes, a bunch of cautious grunts entered the ship.
"Look out for any enemies." Called the major grunt to his group.
The other grunts looked cautiously around the docking bay. The area was quite dark and no one could see quite well. One grunt strayed from the group and bumped into a tank of fuel on the side of the bay for returning fighters, dropships, and other vehicles. The grunt jumped back in surprise.
"Ahhhh! Help me!" screamed at grunt. In his horror, he fired his plasma pistol into it and the tank exploded causing the entire bay to be engulfed in a giant ball of fire. The methane also exploded, causing the dropship to be blasted out of the docking bay and out into space.
The air was immediately sucked out of the bay and the Covenant fighters began to attack the ship. There were still more dropships waiting to board, but the bay was mangled beyond recognition, so most of them returned to the Cruiser. The three destroyers opened fire, and the plasma hit the side of 343's ship, leaving a couple holes in the purple armor. The Covenant cruiser fired a large anti-matter missile directly at the bridge. That will leave a giant hole. he thought. He turned the cruiser sharply to the left as the missile narrowly missed the bridge and disintegrated what were grunt sleeping quarters. The Covenant had him surrounded and they would soon destroy the ship with the constant attacks. If I don't find a way out of this, I will be floating in space again.
The Monitor searched frantically something that could get him out of his current predicament. Does this primitive species even have a form of FTL transport? The builders(of Halo and 343 or Forerunner) often used FTL transport. He searched the control panel for anything that would help him, and found a switch that said in the Covenant language: Faster than light drive. He activated the drive, not expecting much to happen. The ship powered up its reactor and a large hole opened in the blackness of space. The large hole sucked the ship up and quickly closed The Covenant, realizing that the Monitor had escaped and stopped firing furiously at where the Monitor's ship once was. They all powered up their FTL drives and disappeared from normal space.
The Monitor was fascinated by the Covenant's method of faster than light travel. It was not like how the humans traveled, who used Slipstream generators. This method was much more sophisticated, as even he could not understand it. When he was sure that he was safe, he set the coordinates to Halo#2, the ring where another Monitor and his Sentinels were located. It was all too simple: take control of the Sentinels and build a more powerful fighting force.
His plan was almost complete. The Master Chief wouldn't even know what was coming at him. Of course, the Monitor was so caught up in his plan for revenge that he forgot one minor detail: Where was the Chief, anyway?