Battle of the Quarantine Zone
From Halopedia, the Halo wiki
Background info
One of the few four-sided battles of the 9th Age of Reclamation, the Covenant and UNSC fought through the Quarantine Zone to look for the Index, called the Sacred Icon by the Covenant. Both sides had to battle their way through massive numbers of Flood and Forerunner machines: Sentinels and a newly introduced type of Sentinel, Enforcers.
Battle
The Arbiter was sent to the surface of Delta Halo to retrieve the Sacred Icon. The Arbiters main objective was to lower the containment shields, which would allow more Covenant warriors to enter the Quarantined Zone. The shield was deactivated, but this released the Flood to the rest of Delta Halo. This breach of containment led to the rapid growth in the Flood's numbers as they assimilated both humans, from the UNSC In Amber Clad, and Covenant alike. With new hosts, the Flood gained access to more sophisticated equipment, such as personal weapons and combat vehicles. Despite this new and surprising defense, the Arbiter and his squad of SpecOps Elites were able to battle their way trough the countless Flood and Sentinels. After a series of battles the Arbiter regrouped with Rtas 'Vadumee and followed the Humans with a gondola that was headed towards the Library. Rtas 'Vadumee stayed didn't board the gondola, and he stayed behind to keep the flood away from the gondola. Along the ride, the Arbiter and the squad of SpecOps Elites were attacked by numerous waves of Flood and supported by a brute-controlled Phantom before they turned against the Arbiter.
Library
Once the Arbiter and his squad arrived at the Library, the Humans were already inside. The Arbiter's squad of Elites were left behind to guard the gondola since it was their only way out. On his way to the Index he found the dead bodies of Corporal Perez, Private McKenzie, and a few other nameless marines killed by Flood Infection Forms. The Arbiter found the Humans (Miranda Keyes,and Sergeant Johnson), who had retrieved the Index seconds before the Arbiter arrived. The Arbiter head-butted Johnson which knocked out but, before he could get to Miranda, Tartarus showed up along with a squad of brutes and, using his Gravity Hammer, knocked out Miranda and took the index from her. He then blasted the Arbiter off the edge of the platform where the Index was stored, leading Tartarus to make the assumption that he was dead, but was soon teleported by Gravemind.
