There they meet Dr. Halsey who , with help of some of the surviving Spartans , uncovers a strange crystalline shard in a cavern built by the ancient Forerunners .
The surviving Spartans flee underground to the hidden headquarters of the Office of Naval Intelligence .
There Spartans meet Dr. Halsey who , with help of some of the surviving Spartans , uncovers a strange crystalline shard in a cavern built by the ancient Forerunners .
The surviving Spartans flee underground to the hidden headquarters of the Office of Naval Intelligence .