It's been three months since the colony world of Meridian was invaded by the alien alliance known as the Covenant. Under the close watch of the military, Evie, Dorian, Saskia, and Victor have been put into an accelerated training program with ONI, the Office of Naval Intellience. And to the teens' surprise, ONI has a mission for them: return to their hometown on Meridian and monitor the Covenant's efforts to retrieve an ancient Forerunner artifact of untold power.