Outbreak at the Containment Facility

The battle of the Containment Facility occurs on Installation 04, inside a Forerunner structure in a swamp.

Events
The Covenant accidentally released the Flood, and in panic, sealed the Flood in a room deep within the containment facility in order to protect themselves from the horror they had uncovered.

Captain Jacob keyes, along with 2nd Squad landed nearby in Pelican dropship Victor 933 and proceeded to infiltrate the structure. They later met up with Staff Sergeant Avery Johnson's "Fire Team Charlie", who had proceeded to the structure and engaged the Covenant they encountered in the upper levels of the facility. After receiving a transmission from a troubled marine present further into the facility, they set out to provide aid.

While exploring the lower levels, the UNSC forces eventually come across a sealed door, locked down by the Covenant to prevent the escape of the Flood. With increased curiosity the UNSC open the door and explore the room. The Flood attack the UNSC forces and begin to infect any available host present.

Later on, the Master Chief arrived near V933s crash site on board Echo 419. He then entered the lightly guarded structure, being watched by the Flood. After entering the Containment Room, he found Private Jenkins' helmet with camcorder. After seeing the gruesome events through the eyes of Jenkins, the remaining Flood spewed out of nearby doors. John-117 proceeds after the remaining UNSC forces, combating Infection and Combat forms. The Master Chief soon catches up with the remaining UNSC forces, who are advised by Echo-419 to take refuge at a nearby structure, the Library.

The survivors went through the swamp in search of a tower, which would be the Evac site for E419. After making it to the structure, the Marines are aided by a mysterious ally, floating constructs known as Sentinels. The Sentinels, commanded by a Monitor, 343 Guilty Spark, defend the marines, eliminating any Flood in the vicinity of the Library. The Monitor then teleports the Master Chief into the structure, referring to him as "Reclaimer".