Halo: Retribution

Halo: Retribution is a novel by Troy Denning. Having first appeared on Amazon's website, Retribution was officially announced on June 23, 2017, and was released on August 29, 2017. Set in late 2553, the novel follows up on Denning's Halo: Fractures short story A Necessary Truth, although many of the central characters from the preceding novel Halo: Last Light also make a return.

Plot synopsis
In December 2553, Lopis and her Ferret Team are on their first mission, to find the abducted family of UNSC Fleet Admiral Graselyn Tuwa, who was recently assassinated. While disguised, the team gain the trust of a group of Kig-Yar related to the Keepers of the One Freedom, the main suspect. While aboard the Kig-Yar's ship, which is heading to the hidden base of the Keepers, Salvation Base, the Kig-Yar attempt to gas them but the Ferrets take over the ship for themselves, posing as "believers." Meanwhile, Blue Team is tracking the Ferrets in an ONI Prowler called the Silent Joe as a potential backup. Eventually, the Ferrets infiltrate Salvation Base (on a strange Forerunner planet) in search of the Tuwa family.

Olivia-G291 discovers a Turaco ship with evidence of a connection to Dark Moon, which planted the bodies of the Tuwa family within the detention center of Salvation Base to frame Keepers of the One Freedom. A battle occurs when the Ferrets cross paths with the Keepers' leader Castor, but the Ferret escape in the Turaco with Blue Team as Salvation Base is nuked.

Castor, having also discovered the murdered bodies, decides to search for the Dark Moon operatives as well. Although not working together with Lopis, they both follow the trail of evidence back to a laboratory on Gao, where President Arlo Casille admits to having made dealings with Dark Moon. Casille allowed them to use his labs if they promised to deal with the Keepers, who wanted vengeance on Casille after the Gao Conflict. Dark Moon had previously attempted to manufacture a harmful bioweapon from the asteroid compound found at Argent Moon, but they succeeded within the labs on Gao.

After interrogating Casille, the Ferret team to led to Pinnacle Station above Meridian, where A.I. Governor Sloan had initially advised Casille to work with Dark Moon. The Keepers, Dark Moon (now with a manufactured bioweapon), and the Ferrets all collide at Pinnacle Station where a battle breaks out, eventually traveling to the surface of Meridian. Although the Spartans and Ferrets manage to neutralize the bioweapon and Dark Moon, Castor escapes.

After the narrative ends, it is revealed that the Forerunner Ancilla, Intrepid Eye, was behind the bioweapon and Dark Moon. She has been imprisoned on Argent Moon being experimented on and studied, despite ONI at Argent Moon now knowing that Intrepid is in control of the whole station. But, the Spartans and Ferrets never learn this truth, and the true mastermind of the plot is only revealed to the reader.

Trivia

 * The novel's cover is illustrated by artist Benjamin Carré, who also provided artwork for Halo Mythos.
 * Retribution ' s official summary describes the Human-Covenant War as "thirty years of 'intergalactic' conflict". This is an incorrect usage of the term, as the war was never fought in more than one galaxy; a more appropriate word would have been "interstellar", which is defined as occurring between stars. The Battle of Installation 00 was the only battle of the war to be fought outside the galaxy, though not in another galaxy altogether, and the wording in the summary regardless implies the war was waged on an intergalactic scale consistently for its thirty-year duration.