The Spartan-21 team is a faction in Singularity.
In 2010, the United States began detecting large amounts of radioactivity from Katorga-12, an island off Russia's coast that had been shrouded in mystery for years. Fearing another Chernobyl, the United States sent Spartan-21, and elite special forces recon team, to Katorga-12. Before the team could land, an EMP blast caused Nathaniel Renko's helicopter to crash. Renko had to fight his way through the civilian quarters with a Centurion pistol and AR9 Valkyrie assault rifle. Along the way, he had to battle Mutants. He also witnessed his first flashbank/timewave, in which he saves Nikolai Demichev, a scientist who, at that time, had been experimenting with Element 99. Eventually, he reunites with Devlin, one of his fellow teammates. Devlin is killed by Demichev after Renko and him are captured.
If the player chooses to shoot Demichev at the end of the game, the team's members remain alive, as the timeline is altered once again to its original self. However, if the player chooses to shoot Barisov, all but Renko remain dead.