Halo: Reach is a prequel to the Halo series, taking place in 2552 during the events that lead up to and immediately before the events of the first game, Halo: Combat Evolved.
The game takes place on the titular planet of Reach, it is the UNSC's last major stronghold outside of the Sol system and home to some 700 million human civilians. Now, despite the UNSC's best efforts to keep its location secret, the alien alliance known as 'The Covenant' have located it and launched a full scale offensive against Reach. The player takes the role of the Spartan-III super soldier SPARTAN-B312, who forms a part of Noble Squad and operates under the callsign of 'Noble Six'. With Covenant forces systematically taking over Reach, you must fend them off.