The climactic battle for the Halo begins. John makes a fateful choice. Soren and Kwan undertake a rescue mission. Halsey and Miranda unleash an ancient horror.

John seeks revenge on a secret ONI planet. Perez trains to become a new kind of soldier. Kai finds herself torn between her Spartan code and her loyalty to Master Chief. Makee turns to Cortana for help in her search for the Halo.

John-117 comes face to face with Makee. A revelation leads Ackerson to question his loyalties. Soren and Laera's relationship begins to fracture. Halsey, Kwan and Miranda work to solve a mystery.

A Covenant assault threatens humanity's most important stronghold. John, Perez and Silver Team fight an overwhelming enemy. Adm. Keyes rallies the UNSC forces to make a stand. Halsey and Soren must work together to escape captivity.

In the aftermath of defeat, the survivors struggle to pick up the pieces. On the desolate planet of Aleria, John grapples with an unprecedented loss. Soren and Laera search for their missing son. Makee treads carefully as the Arbiter grows impatient.

A deadly evacuation mission signals a shift in Master Chief's war with the Covenant. On Reach, a new regime takes the reins at FLEETCOM. John senses a looming threat close to home.

John pushes Silver Team to its limit as he searches for missing Spartans; Kai worries about John's stability. Kwan finds the Rubble is a far more dangerous place in Soren's absence. Halsey seeks the identity of her captor.

John and Silver Team embark on an unsanctioned mission. Laera, Kwan and Kessler must escape Soren's mutinous crew. Ackerson receives troubling intelligence from Cortana. The threat of an attack forces Ackerson to make an irrevocable decision.