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.
In the year 2552, humans on the planet Madrigal fight 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.
Survivors of the battle with the Covenant return to Reach. John confronts Dr. Halsey and her lies. The new prisoner seems to know John better than he knows himself. The mysterious artifact shows John something 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 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 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. Season premiere.