Fireteam Osiris

"Osiris" redirects here. For the Halo 5: Guardians campaign level, see Osiris (level).

"We are the shield between humankind and danger."

- Spartan Jameson Locke

Fireteam Osiris is a specialized combat and intelligence gathering team of Spartan-IV supersoldiers of the Spartan branch. The team carries out complicated and classified missions for the Unified Earth Government and its United Nations Space Command, typically dealing with issues that are deemed hard to control by the UNSC High Command. Fireteam Osiris' activities are classified at the highest levels of government.

Members
Fireteam Osiris is composed of four of the most prominent and effective personnel from throughout the different branches of the United Nations Space Command. Osiris' members were selected based on their skills, with the desired outcome being that each team member's skills would mitigate another's deficiencies. The fireteam's balanced skillset and impressive success rates causes them to be commonly deployed in extremely sensitive and complex missions.
 * Jameson Locke – Team leader; former acquisitions specialist for the Office of Naval Intelligence.
 * Olympia Vale – Former UNSC Navy intelligence officer and xenoanthropologist.
 * Holly Tanaka – A highly skilled engineer; former member of the UNSC Army Corps of Engineering.
 * Edward Buck – A former Orbital Drop Shock Trooper, and the advisor and mentor of the team.

Rescue and assassination
In October 2558, Fireteam Osiris was deployed from low orbit to rescue Dr. Catherine Halsey, who had sent the UNSC a distress call while in Covenant custody. Tracked to the planet Kamchatka, the Spartans landed amidst an enormous battle between Covenant and Promethean forces, using the chaos from the droids' sudden rebellion to cross through enemy lines. Osiris eventually reached Halsey at a Forerunner temple, accompanied by Covenant supreme leader Jul 'Mdama. Vale, Tanaka, and Buck fought Jul's Zealot guards while Locke fought Jul himself, ultimately killing him and bringing Halsey safely back to the.

Hunting the Chief
Later that day Blue Team, the veteran Spartan-II unit led by the Master Chief, went AWOL shortly after messaging a mysterious message from Cortana telling them to go to Meridian. Fireteam Osiris was sent to retrieve the Spartans, and were given use of armor restraint devices to disable Blue Team's armor.

When they arrived Meridian, Fireteam Osiris was met with much hostility from the planet's citizens and their governing AI Sloan. However, the Spartans earned grudging acceptance from them after defeating numerous Promethean forces attacking the miners. After the battle, the Spartans asked around the local residents and learned that Blue Team had last been seen near Apogee Station. Finding Blue Team's abandoned prowler there, Osiris searched its onboard data and found a nearby mine that appeared to have been of interest to Blue Team. The Osiris Spartans traversed through the mine and at the end found a subterranean chamber with Forerunner ruins, holding an enormous inert Guardian and protected by a construct calling itself the Warden Eternal. And as Osiris had suspected, Blue Team was also there. After fighting the Warden and his Prometheans, Fireteam Osiris confronted Blue Team, with Locke himself battling the Master Chief. However, Blue Team refused to stand down or surrender, and Osiris was forced to flee the ruins after the Guardian activated and began collapsing the cave in its attempt to break through to the surface.

Returning to Meridian Station, Osiris aided the fleeing settlers as the Guardian and Prometheans wreaked havoc on the collapsing town. The Spartans narrowly escaped when the Guardian's EMPs severely damaged the local space elevator, and eventually returned by Pelican to the Infinity.

Alliance on Sanghelios
Having learned that Cortana was awakening the Guardians and calling them to an unknown location, the UNSC formulated a plan to catch up to her and Blue Team. By taking control of an inactive Guardian on Sanghelios, Infinity could feed it coordinates they had gleaned from the Guardians' signals, let Osiris climb aboard, and then send to wherever the others were headed. Doing so would require the aid of their former-Covenant allies, the Swords of Sanghelios. As their leader the Arbiter was being attacked by the remnants of Jul's followers, Osiris was deployed on Sanghelios to rescue him, fighting a pitched battle through Covenant attackers while aboard Mantis mechs, successfully reaching him and escorting to a safe location.

At the Arbiter's forward operating base, Locke negotiated with Thel 'Vadam on their plan of attack. They reached on an agreement on assaulting Sunaion when victory would be assured for the Swords of Sanghelios. Dr. Catherine Halsey found the means to activate the Guardian by using a Constructor. The Constructor was stored in a support station for the Guardian, and so Osiris deployed to retrieve it. After a lengthy battle, involving a Kraken, the Constructor was retrieved and the plan could move forward. Right before deploying for the hit on Sunaion, Halsey demanded to Osiris to bring back John, and stop Cortana.

The assault on Sunaion commenced and Osiris was brought steps closer to the Guardian. The Prometheans and the Warden Eternal got involved near the climax of the battle, but they were dispatched. Sarah Palmer came in with assistance to bring Osiris up to the Guardian via a Pelican, with Osiris jumping out of the dropship to board the Guardian. With Osiris on board, Guardian then made a slipspace jump to Genesis, while the Blooding Years concluded on the streets of Sunaion.

Trivia
Osiris was an Egyptian god of the afterlife, the underworld, and the dead.

Production notes

 * Fireteam Osiris is featured in Halo 5: Guardians. They accompany Locke throughout the campaign and accept commands from the player. Buck, Tanaka, and Vale are playable in cooperative play, each with a specialized default loadout. The team has access to the Artemis Tracking System which can highlight alternate routes as well as various items of interest.
 * Buck's place as the fourth member of Fireteam Osiris was filled by Gabriel Thorne in an early phase of the development of Halo 5: Guardians. Due to Ethan Peck being preoccupied with another television series, Thorne was replaced by Buck later on after Nathan Fillion agreed to reprise his role. Thorne is still shown alongside the members of Osiris in an early piece of artwork featured as the cover of The Art of Halo 5: Guardians.

List of appearances

 * Halo 2: Anniversary
 * Halo: New Blood
 * Hunt the Truth
 * The Hunt Begins
 * Halo 5: Guardians
 * Limited Edition