Sacred Icon is the Eighth playable level. This level, once again you are the Arbiter. The task is to get to the Quarantine Zone by killing all the flood in your path. This mission begins a set of missions centered around the Sacred Icon and Flood elements of the Halo storyline. The premise behind this storyline is that you are retrieving the Halo Key from a Flood infested station. You can expect the entirety of the missions comprising this goal take place in often dark areas infested with hordes of Flood.
This first segment will bring you through areas where many Carrier form and Combat Flood will attack you in waves. In terms of difficulty this is an easier, but still potent part of the Sacred Icon missions.
 Uncomfortable Silence
In this part of the station, and in fact all parts of the Sacred Icon portion of the campaign, a shotgun is the most effective weapon against all Flood except for the Infection form. The shotgun will kill all Flood with a single, close range bast in Normal mode.
Later this is not true, so take advantage of this while you can, but also, try to preserve shotgun ammo where possible, as you will be in dire need of it in the mission "Quarantine".
At the end of this mission you will face your first Forerunner Enforcer. The Enforcer has potent front shields and powerful weapons, but it moves slowly and its weapons are also slow. Keep under it on the lower level of that area, so that it cannot see you, and maneuver yourself until you have a clear shot at its unprotected sides, underside, and back. You will have to move repeatedly to take care of the Enforcer since your weapons will not make quick work of it.
 Buyer's Remorse
Your objective in this mission is to "Make your way through the Flood infested Wall", which is basically what you have to do. The mission is straightforward and does not need excessive walkthrough information, but you can expect a few things and should employ the same strategies as usual to deal with them:
- There are plenty of Flood in this mission, including Infection flood.
- Use a Shotgun, Sentinel Beam, and (if you like), Energy Sword to deal with most of the Flood.
The begining of the mission starts you off entering an area where there are many Flood fighting Sentinels. This part is one of the more tricky parts of the level, and one strategy is to allow the Sentinels to do their job and stay underneath in the lower level of the docking bay to avoid attracting the attention of the Sentinels. Eventually you will get a checkpoint and somehow one of the large bay doors will open and you can hop through. It seems that the Flood will continue to appear for a LONG time so don't stay around to kill all of them, just enter the bay door when it opens.
After that first part the mission is very simple, just fight your way until you reach the next stage.
 100,000 Year's War
Your objective in this mission is to make your way and join your allies in the Covenant camp. This is one mission with a stunning backdrop in the distance.
You start the mission with Elites joining you as reinforcements. Let them take care of any Infection flood that come your way so you can safe ammo for larger enemies.
This is actually a very short mission, and ends after you defend the base camp against a small number of Flood (in Normal Mode). The next mission "Quarantine Zone", will be one of the hardest missions you've attempted yet!
"Arbiter, this Quarantine zone has been compromised. We must do what we can against the Flood. Our Commander has landed farther in, let us join you".