Halo: Alpha-Nine Books in Order

Edward Buck looks back on the combat service that he and his ODST squadmates gave during the Covenant War. After the conflict, and amid losses among the Spartans, the UNSC offers Buck a choice that could turn the veteran soldier into part of a new Spartan generation.

In the aftermath of the battle on Genesis, Spartan Edward Buck is pursued by the newly rogue AI Cortana. A covert ONI assignment forces him to reunite Alpha-Nine, including a former teammate whose betrayal has left lasting wounds.

Following the events on Genesis, Spartan Edward Buck and his allies flee the now-rogue Cortana. An Office of Naval Intelligence mission compels Buck to reunite Alpha-Nine, forcing the team to confront both a new crisis and an old betrayal.