The 26th century. Humanity has expanded beyond Earth’s system to hundreds of planets that colonists now call home. But the United Earth Government and the United Nations Space Command is struggling to control this vast empire. After exhausting all strategies to keep seething colonial insurrections from exploding into a full-blown interplanetary civil war, the UNSC has one last hope.

2559. It has been a year since the rogue artificial intelligence Cortana seized control of the Domain, an otherworldly dimension housing a vast information network. With an array of Forerunner weapons at her disposal, Cortana set out to enforce an authoritarian peace on the civilizations of the galaxy. But as the United Nations Space Command flagship Infinity prepares to strike against Cortana at Zeta Halo, another plan has also been set in motion.

As kids, the three of them were inseparable; as soldiers, they would be torn apart. Marcus Fenix and Dominic Santiago fought alongside Dom’s elder brother Carlos at Aspho Fields in the epic battle that changed the course of the Pendulum Wars. There’s a new war to fight now, a war for mankind’s very survival. But while the last human stronghold on Sera braces itself for another onslaught from the Locust Horde, ghosts come back to haunt Marcus and Dom.

On the planet Tython, the ancient Je’daii order was founded. And at the feet of its wise Masters, Lanoree Brock learned the mysteries and methods of the Force - and found her calling as one of its most powerful disciples. But as strongly as the Force flowed within Lanoree and her parents, it remained absent in her brother, who grew to despise and shun the Je’daii, and whose training in its ancient ways ended in tragedy. Now, from her solitary life as a Ranger keeping order across the galaxy, Lanoree has been summoned by the Je’daii Council on a matter of utmost urgency.

After discovering a cache of Prothean technology on Mars in 2148, humanity is spreading to the stars---the newest interstellar species, struggling to carve out its place in the greater galactic community. On the edge of colonized space, ship commander and Alliance war hero David Anderson investigates the remains of a top secret military research station---smoking ruins littered with bodies and unanswered questions. Who attacked this post, and for what purpose?