In the 26th century, the Covenant, an alliance of alien races, seeks to destroy humans using the superweapon Halo. Humans, led by Master Chief and the U. N. S. C. , train Spartans on Reach to fight back. Master Chief's connection to A. I. Cortana jeopardizes his life, pushing him to sever ties. As he faces Covenant forces with his team, a former Spartan falls into a trap while investigating Dr. Halsey, who interrogates girls involved in a sinister plot. Tensions escalate as mysteries unfold, including the reappearance of an ex-girlfriend suspected of betrayal.