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.

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.

On the run and out of options, Kwan and Soren have a difference of opinion. With the possibility of finding the mysterious Halo on everyone’s minds, John makes a horrible discovery. And the war rears its ugly head.

Beaten, battered, and betrayed, John 117 leads the Spartans on a suicide mission to find the Halo and save humanity. But at what price?

In the year 2552, humans on the planet Madrigal have been fighting for independence from Earth, but a fatal encounter with the Alien Covenant complicates things. Master Chief John 117 and his super-soldier “Spartans” join the fight. After the battle, Master Chief heads to his home planet of Reach with a Madrigal survivor and a mysterious object he discovered on the planet. But a controversial order has John questioning his mission, and himself.

Survivors from battle return to Reach. John confronts Dr. Halsey, and the lies of his past. The new prisoner seems to know John better than he knows himself. Determined to understand more, John turns back to the mystery artifact, which shows him something truly startling.

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.

John and Makee come to terms with their shared vision. Halsey has one last chance to save her mission, and herself. As things come to a head, everyone must choose a side.

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 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 meets his new partner, and he discovers secrets inside his own memory. Kwan wants to return to Madrigal to continue her people’s fight for independence, but Soren has other plans for her. Makee initiates her plan to retrieve the Madrigal object, with deadly consequences.

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 takes Kwan to an old friend and learns more about the mystery object, which the Covenant and Makee are determined to steal. With the alien threat growing, Dr. Halsey has a plan to deal with John’s unpredictable behavior.

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.

Guided by his visions, John takes Halsey and Cortana back to where it all began, looking for answers from his past. With Soren along for protection, Kwan goes in search of an army. Meanwhile John’s behavior inspires another Spartan to begin a journey of self-discovery. And Miranda discovers a possible link between the artifact and something much larger.

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.

Kwan’s journey to uncover her family’s “true purpose” takes her deep into the deserts of Madrigal. Soren obsesses over unfinished business.