Cal, Letty, Tony, Opi, and Sasha were kidnapped by the Molethian civilization and trained to fight against The Horde—the greatest threat in the Milky Way galaxy. They rise quickly through the ranks of the space service and accept increasing responsibilities that fit their talents. While his friends take on leadership positions closer to home, Cal disappears on a mission to the Horde galaxy and is presumed dead. Horde invasion fleets roam the Milky Way, looking for Alliance home planets. Unfortunately, Earth is not yet ready to join the Alliance. When Letty tries to persuade them to join by meeting with one of its recalcitrant countries, she suddenly goes missing. Meanwhile, a huge Horde Fleet shows up on the outskirts of our solar system, apparently planning a deadly attack against Earth. With Cal and Letty both missing, Tony, Opi, and Sasha rally together to lead Alliance forces into what may be their final battle!