Halo: Ghosts of Onyx
From Halopedia, the Halo wiki
Halo: Ghosts of Onyx is the title of the next Halo book by Eric Nylund. Published by Tor, it is due to be released on October 31st, 2006. As of yet, nothing more is known about it, although it may have something to do with Dr. Halsey and Kelly, as well as CPO Mendez, and the possible next generation of Spartans.
Through the leak of the working title, "Halo: Ghosts of Coral", it was speculated to be about the planet Coral, which is the site of excavations that have uncovered Forerunner artifacts (see Conversations from the Universe), though this speculation is most likely not valid because of the announcement of the real name.
In addition, the announcement of the title also included a confirmation that Ghosts of Onyx is not the last planned Halo book. At least two more novels are planned to follow it, this is part of the contract with Tor.
