[7] IGN's reviewer, Douglass C. Perry, found that by using short paragraphs and many jumps in time "[the novel's] style of writing keeps the pace going, even when nothing much is going on.

"[9] Ghosts of Onyx takes place in the 26th century, where humanity, under the auspices of the United Nations Space Command, has developed faster-than-light travel and colonized hundreds of worlds.

Humanity's best weapon against the technologically superior Covenant are the SPARTAN-IIs, supersoldiers equipped with biomedical augmentation and powerful armor; unfortunately, there are too few of the SPARTANs to turn the tide of the war.

Ackerson announces his plan to create a new breed of SPARTANs which retains much of the supersoldiers' effectiveness, without the high price tag of the SPARTAN-II program.

The SPARTAN-III project is carried out on a secret ONI planet named Onyx, where there is also an archaeological excavation of ancient Forerunner ruins in an area known as "Zone 67".

Like the SPARTAN-IIs, the SPARTAN-III candidates undergo radical cybernetic and biological enhancements and are outfitted with special armor to increase their abilities.

Halsey identifies the robotic drones as Forerunner Sentinels from the artificial intelligence Cortana's logs of the events of Halo: Combat Evolved.

The entire UNSC fleet at Onyx is destroyed by the ensuing battle, save for one stealth ship, the Dusk, which stays hidden, observing the events.

The remaining human forces on Onyx discover a Forerunner city being rapidly uncovered by the Sentinels, and are guided into a massive sphere by Dr. Halsey.

She determines that the entire planet is actually a "Shield World" constructed by the Forerunners to protect themselves from the firing of the Halo ringworlds, which are designed to eradicate all sentient life.

[8] The publication did note, however, that the Master Chief made only a cameo appearance, and that Ghosts of Onyx is "about the supporting cast of characters", rather than the heroes of the video game.

[8] Offering a less positive outlook on the book were publications like Subnova.com, which blasted the novel as being much worse than Halo: First Strike, introducing characters the reader didn't care about and using too much jargon.