Master Chief takes temporary refuge in a place called The Rubble. The Rubble is just outside a minefield and is filled with what another film might call "villainy and scum" who can't be safe anywhere else.
The Rubble is ruled, in a way, by Master Chief's old classmate Soren-066. Soren escaped Spartan training years ago, though just barely so, since John was thoroughly indoctrinated in the Spartan program, and it was either kill Soren for disobeying orders or let him have a short head start before sounding the alarms.
Soren has a section of his sprawling space city full of people who seem insane. Among them is a man who was captured by the Covenant and got away. He mostly babbles but he takes to Kwan Ha, the teen refuge right away. He can't tell them much except the artifact can lead to another object the Covenant want, a ring.
Master Chief again touches the artifact, causing waves of something blue to roll through the area, causing the inmates to scream. Reth declares Master Chief a "Blessed One" because he can interact with the object.
Also a Blessed One, a mysterious girl who is revered among the Covenant asks to go into the human territory to get the "keystone" which will lead them to the ring.
Master Chief leaves a reluctant Kwan Ha with Soren and goes back to the Reach and turns himself in.
Here he's imprisoned but gets a visit from Halsey who tries to find out more about the artifact and what the changes Master Chief is experiencing mean.
She's cleverly manipulated the UNSC council to allow her to try out Cortana, a clone (?) of herself who is the next level above the Spartans and who can be controlled and control the Spartans. I think that's right :)
Lots of characters to know, a complicated society, an implacable enemy. What's not to like?