Halo: Envoy is a novel set in the Halo universe by Tobias S. Buckell. It was released on April 25, 2017. The Halo: Fractures short story Oasis, also written by Buckell, served as a quasi-prequel to Envoy, introducing the novel's central setting and conflict.
Melody is dispatched as an envoy to the Sangheili Fleetmaster Rojka Kasaan who is a commander in the Joint Occupation Zone of planet Carrow. She comes to find that the ship master is in possession of the Spartans known as Gray tTeam. He had collected them (in secret) after the destruction of Glyke due to Operation: SUNSPEAR. Due to civil unrest among the conflicting Sangheili, Rojka is distracted and Melody is able to sneak off to the storage room Gray Team is being held in. She manages to improperly thaw the three Spartans from cryo sleep just before being rendered unconscious from wounds inflicted by guards of Rojkas'.
Melody awakes to find herself in the presence of the infamous Gray Team. She realizes that Gray Team is somewhat in the dark about their current whereabouts and situation. They come to find that the Human-Covenant War has been over for more than six years and that they have been in cryo the whole time as prisoners to the Sangheili Rojka. Gray Team discovers they have left a dire situation stranded in space only to be brought back right in the middle of the fray of a new and desperate situation. They learn of the new JOZs and that humans and Sangheili are residence of the planet they are now seemingly stranded on.
Struggling to come to terms with their past actions concerning the activating of the NOVA Bomb, Gray Team now tussles among themselves as they try to grapple the reality of their new situation. While continuously being perused by the obsessed and irate Rojka, Gray Team and Melody start trying to find their way through the desert of Carrow toward a rendezvous previously set up with Melody. Gray Team and Melody finally make it to the pre-scheduled meeting location only to find an underground ONI facility buried in the mountains. They narrowly gain access to the base just before being destroyed by Rojka and his followers. Soon Rojka blasts his way into the base and forces Gray Team on the move again.
Out of the base and back out in the sand Gray Team and Melody make their way to the nearby human settlement which is currently in a battle. Once in town they discover there is more distress lurking besides the vengeful Fleetmaster. A radical Jiralhanae, Hekabe, supposedly under the authority of Rojka, decides to set his plan in motion. He ignores Rojka's orders and brings his ship and army to the surface of Carrow and begins his plot.
Gray Team and the local human government realize that Hekabe has started digging in the desert so they put plans in action to intercept him. Their plan to thwart Hekabe finds much resistance as the jiralhanae continue burrowing deep into Carrow toward an ancient and forgotten terror, the mythical Sharquoi. Upon discovering his goal to try and control the Sharquoi, Melody, Gray Team, and the human government enact a daring mission to intercept Hekabe. Their mission takes them to the edge of despair as they close in on Hekabe and find that they're too late. Hekabe, with the help of an anciet artifact, is able to control the mythical monsters and pit them against the humans. Gray Team and company direly challenge the enraged Jiralhanae and his thousands of Sharquoi in the depths of the forerunner structure under the desert sand. They narrowly escape the destruction of the structure and bury the remaining horrors deep underground.
Gray Team and Melody are taken back into UNSC custody once reinforcements are able to access the planet. Melody is congratulated for securing Gray Team and acting as envoy and is then sent to be debriefed by ONI. Gray Team are debriefed and caught up on the six years they were in cryo. They learn that Operation SUNSPEAR was actually conducted after the peace treaty with the Sangheili and that the Covenant has been dismantled officially. Gray Team is then given a choice whether they want to be discharged from the UNSC or be put back into operation. They choose to stay active at the behest of a few requests, which CINCONI, Admiral Serin Osman a fellow Spartan-II, quickly agrees to.