Battle of the Quarantine Zone
From Halopedia, the Halo wiki
Background info
The Flood have escaped because the Arbiter turned off the Containment field, so the Sentinels are attemping to kill the flood. Miranda Keyes moves in with a load of Marines to secure the Index, but are met by Flood who halt their progress. By now the Arbiter has met up with the Spec ops Commander,and they go to secure the Index as well. The Flood and Sentinels fight it out and the Arbiter succeeds in retrieving the Index. Arbiter wins, only to be blown off the edge by Tartarus.
