The third season begins seven months after the Second Independent Regiment arrived in Charleston. During this period, Charleston was designated as the capital of the "New United States of America", and Tom Mason was elected as the political leader (equivalent to the president). But most of his time was not in the office to handle government affairs, but leading the army to stubbornly resist the repeated attacks of alien invaders. Compared with his predecessor Dr. Manchester, Tom is more aggressive and proactive in his attitude towards aliens. The Charleston government has formed an unreliable alliance with the rebellious "Raiders". Tom lets the "Raiders" rebels stay in Charleston to fight alongside humans, but this has caused some dissatisfaction among humans, and the relationship between the two races continues to be tense. The "Raiders" rebels always paint their faces with red and yellow stripes before the battle to commemorate the leader "Red Eye" who died heroically at the end of the second season. Tom's son Ben is now the liaison between the Charleston government and the "Raiders" rebels. Both humans and "Raiders" understand that it is difficult for them to defeat a powerful enemy even if they join forces-the alien race Espheni, which was previously nicknamed "fish heads" by the Second Independent Regiment. Although their king is dead, another more powerful and evil king has just inherited the throne. To make matters worse, a new alien race has arrived on Earth in the heat of the battle and quickly joins the fight.