Percursors!
It has been announced that the next to Halo books will reveal stuff that will be related to Halo 4.
Halo Primordium (sequal to Cryptum): Set primarily on the "rogue" Halo ring used by Mendicant Bias during the events of Halo: Cryptum, the novel follows the journey of the humans Chakas and Morning Riser, former companions of Bornstellar Makes Eternal Lasting. After crash-landing on the Halo ring during Mendicant Bias' assault on the capital, they discover it has been used by the Master Builder's researchers to conduct research on humans. They are forced to make their way across the embattled Halo installation, facing the Flood and rogue AI constructs on the way, while the Precursors' ancient plan of vengeance against the Forerunners is revealed. During their journey, they find their way into the Palace of Pain, the lair of the ancient entity known as the Timeless One, which has unleashed the Flood on the Master Builder's researchers on the installation. Mendicant Bias will also play a major role in the story.
Frank O'Connor has mentioned that the story is "closer to the ground" than that of Cryptum, and that it will have "resonant connections" to Halo 4. Greg Bear has hinted at a connection between John-117 and one of the novel's human characters. He also confirmed that the novel will explore the Precursors' plan, and that it may cover events that occurred up to three billion years before the events of Halo: Combat Evolved.
Halo Glasslands (sequal to Ghosts of Onyx. Takes place after Halo 3): Set after the events of Halo 3 in 2553, Halo: Glasslands will explore the volatile political situation in the Halo universe following the end of the Human-Covenant War. Though the story of the characters from Ghosts of Onyx will be continued in the novel and they will play a pivotal role, Frank O'Connor mentioned that the focus of the story moves into "something really different"; a UNSC black ops team sent by the Office of Naval Intelligence on a diplomatic mission to Sanghelios. Led by Captain Sarah Osbun, a failed SPARTAN-II candidate and a protege of ONI director Margaret O. Parangosky, the team consists of two Orbital Drop Shock Troopers, Vaz and Mal, and the AI construct Black Box. They are accompanied by a civilian academic known as Evan Phillips, who is notably one of the few humans fluent in the Sangheili language. The team's allegiances are tested as they are asked to commit questionable actions, including surrendering a captured Huragok to the ONI. At one point, they meet with the survivors from the Battle of Onyx.
It has also been mentioned that the Office of Naval Intelligence will be fleshed out and the moral implications of the SPARTAN-II Program and those involved with it - including Dr. Catherine Halsey - will be explored. In addition, Sangheili culture and the impact the sundering of the Covenant had on their society will be explored in detail.
It has been noted that threads of the story will have connections to Halo 4.
The Source for these was at Halopedian.com http://www.halopedian.com/Main_Page
[Edited on 07.29.2011 8:58 AM PDT]