"Dark Sector" begins with Hayden Tenno infiltrating a gulag compound in Lasria. Hayden makes short work of enemy resistance to find Robert Mezner, the man responsible for ravaging Lasria with the Technocyte virus. Hayden proceeds with planting C4 charges throughout the building, before encountering a humanoid metal figure called Nemesis. Hayden is knocked unconscious after firing a rocket at Nemesis. Waking up hours later, Hayden finds himself face-to-face with Mezner. As Hayden attempts to reach for his gun, Nemesis appears and stabs his right shoulder, transferring the Technocyte virus into Hayden. Hayden detonates the C4 charges set earlier and manages to escape.