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Hastati Squad, the newest batch of freshman cadets at the UNSC's Corbulo Academy of Military Science, pays the price for cadet Thomas Lasky's tactics.

Cadet Michael "Sully" Sullivan continues to decode the hidden ONI combat video as Lasky's struggle with his place in the UNSC ignites with fellow cadet Walter Vickers. After a classroom confrontation with Captain Mehaffey and a challenge from Chyler, Lasky pulls Hastati Squad back from the brink...at a terrible physical cost to himself.

Sully's illicit intelligence video shows Hastati Squad that their world is even more complicated than they knew. Lasky’s collapse at the end of his brilliant field maneuver turns into a pivotal choice for him, and just as he and Chyler realize what that choice might mean for their relationship, the academy is shaken by the first blow of a terrifying invasion.

While Corbulo Academy is being destroyed by the Covenant invasion, the surviving cadets fight bravely alongside their only hope: The Master Chief.

After a terrifying night of combat and loss, Lasky makes a life-or-death decision to help the Master Chief... but will it be enough to save them all from the Covenant?