Over the course of Halo 5, Master Chief searches for Cortana, who mysteriously appears to him in a vision. Unfortunately, that means going AWOL from a UNSC that's grounded him. So, the shadowy Office of Naval Intelligence sends their best agent, Locke to hunt his team and him down. This hunt is disrupted by the awakening of massive Forerunner constructs called 'Guardians,' a civil war on the Elite homeworld of Sanghelios and culminates on a Forerunner builder world called Genesis.
Dozens, if not hundreds, of the massive Guardian constructs have returned to Genesis to await orders from their new leader: Cortana. Thought dead at the end of Halo 4, sacrificing herself to help Master Chief defeat the mad Forerunner leader known as The Didact, she's returned. But she's actually replaced The Didact, and plans on using the full might of Forerunner technology to bring peace to the galaxy. The Guardians are weapons that she plans to use to keep all sentient races in check.
Unfortunately, that doesn't fly well with Chief or Locke, so they team up to stop her. And so, the war between AI and biological life begins. Halo 5 ends with Chief and Locke trapped on Genesis, Cortana on the warpath, and humanity retreating.
At E3 this year, we saw a peek at the game's sequel: Halo Infinite. Said to take place a few years later, The Master Chief will fight on a Halo ring once more, specifically Installation 07, home to many secrets of Forerunner and Flood alike.
So, how do we get from Genesis to Installation 07?
Halo: Bad Blood, a novel written by Halo veteran Matt Forbeck picks up immediately after the events of Halo 5, and lets us start to piece together the road to Halo Infinite.
Obviously, there are spoilers ahead. If you plan on reading the book, maybe skip the article. If reading expanded lore books isn't your thing, though, here's a quick TL;DR.
We follow a familiar face in the form of Nathan Fillion's character, Buck, the ex-ODST now on Spartan Locke's fireteam. Blue team and Fireteam Osiris need a ship to escape Genesis. Exuberant Witness, the monitor of the builder world, helps them find human ships that were pulled to the world by the Guardian's portals.
They find a Pelican, and Witness gives them a portal to Sanghelios, where their last mission was, hoping to regroup with the UNSC. Unfortunately, the planet's Guardian has destroyed much of the Sangheli fleet and left their cities in ruins.
They regroup with The Arbiter, Sarah Palmer and Dr. Halsey, who let them know that the UNSC flagship -The Infinity- will meet them near one of Sanghelios' moons. The Infinity's currently being hunted by Cortana, but Captain Lasky's kept clear so far. Better yet, he's got the crew from Halo 3: ODST onboard for Buck to make his reunion since the events of his last book, Halo: New Blood. Or at least most of them. Don't want to spoil the last book, but yeah, a few of them didn't make it.
Master Chief and The Arbiter enjoy a barbecue courtesy of The Elites, forever leaving us with the image of Chief and Arby throwing beef on the barby while bro-ing it up over a pile of beers.
They rendevouz with the Infinity which, as it turns out, is now the central command center for the UNSC's effort to eventually fight back. Buck leaves the Infinity to reach out to human insurrectionists who weren't super friendly with the UNSC, but might reconsider facing annihilation from Cortana's AI regime. At this point, the story branches away and we follow Buck. If you want to hear his story, I'd absolutely recommend reading the book.
Master Chief and Locke are now onboard The Infinity, working on plans to fight back against The Created (the name the AI regime has chosen for their kind).
It's still unclear how exactly Master Chief finds himself on Installation 07, with a suit of classic Mark VI armor. With Halo Infinite probably releasing next Fall, I think we'll see more of that story unfold in upcoming Halo novels.
Until then, 'Bad Blood' is a good Halo story that pushes the universe past one of its more awkwardly told eras, into territory I can't wait to see more from.