Fireteam Osiris are dispatched to recover the UNSC’s most wanted criminal: Doctor Catherine Elizabeth Halsey

The Master Chief is reunited with his Spartan II Blue Team for a routine investigation of the lost ONI research station Argent Moon

Osiris must pursue Blue Team to a glassed world beyond UNSC jurisdiction

Osiris learns that Meridian Station harbors many secrets

Osiris track Blue Team deep below the surface of Meridian

Osiris are separated from Blue Team and must race to catch up

Blue Team arrive at the Forerunner world Genesis, where they discover the true reason for the Guardian’s activation

When evidence reveals the Master Chief is in danger, Fireteam Osiris’ mission changes from retrieval to rescue

Osiris joins forces with the Swords of Sanghelios

In order to activate the Guardian, Osiris must track down a Forerunner Constructor

Osiris and the Swords of Sanghelios prepare for a final battle with the Covenant

Osiris race to reach the Guardian before it leaves Sanghelios

Osiris arrive on Genesis, where they meet a new ally in their battle

The Master Chief and his team face their greatest threat, and his hardest choice as the true power of Genesis is revealed

As Blue Team’s lives hang in the balance, Osiris must save them and stop the Guardians