Titanicus

A standalone novel by Dan Abnett, set in the Warhammer 40000 universe. When the vital forge world of Orestes comes under attack by a legion of Chaos Titans, the planet is forced to appeal for help. Titan Legio Invicta, although fresh from combat and in desperate need of refit and repair, responds, committing its own force of war engines to the battle. As the god-machines stride to war, the world trembles, for the devastation they unleash could destroy the very world they have pledged to save.

As part of Warhammer 40000, the novel involves a large number of the tropes on that page, as well as employing literary and narrative tropes of its own:

 * Anyone Can Die: It's a Dan Abnett novel.
 * Artificial Limbs: The members of the Adeptus Mechanicus are augmented to varying degrees.
 * Bar Brawl: A drunken Stefan kills a man from Tanith after he indirectly badmouths Cally.
 * Book Burning: burns any sequestered book that comes his way that might threaten the Imperium. It's how the conspirators suss out that he'll never side with them, as they are the ones leaking the books.
 * Civil War: The revelation about the God-Emperor and the Omnissiah threatens to split both the Imperium and the Mechanicum, as well as fracture the Mechanicum itself. Civil war is only narrowly averted by the novel's end.
 * Covers Always Lie: There are no Space Marines in this book.
 * Doomed By Canon: The conspirators of Orestes plan on divorcing Mars and Terra. Considering what we know about the future of WH40K, they obviously can't succeed.
 * Heroic Sacrifice: . Meanwhile,.
 * He Knows Too Much: Feist, Kalien, and . Only the latter gets offed, however.
 * Humongous Mecha: It's Imperial Titans verses Chaos Titans on a scale rarely seen since the Horus Heresy.
 * Irony:
 * Just Between You and Me: Feist earnestly requests that the conspirators explain their plan to him before they kill him, and then they do so.
 * Madness Mantra: "The magnos organos's name was Kercher."
 * Machine Worship: While all the members of the Adeptus Mechanicus engage in this practice, Titanicus sees the debate on the theological relationship between God-Emperor and the Omnissiah reach a breaking point. The members on Orestes generally see the Omnissiah as a separate being, while the members of Legio Invicta see them both as the same. Also, at several points, a few people on both sides of the ideological divide roundaboutly argue -- to avoid open heresy -- that it doesn't matter if the God-Emperor isn't the Omnissiah; Mars and Terra can't endure independent of one another, and attempting to divorce them will just invite extinction for both.
 * Nice Job Fixing It, Villain: The surprise attack conducted by the second armada of Chaos engines helps to avert a civil war that could possibly have destroyed the Imperium and driven humanity to extinction. To be fair, they weren't exactly in a position to know an Enemy Civil War was about to break out.
 * Take Our Word for It: The reader is not told how the God-Emperor and the Omnissiah are proved to be completely unrelated, only that the evidence is pretty much bulletproof.
 * Unstoppable Rage: Tarses snaps and kills the magos organos who tells him his princeps died during transit. He feels immense regret about it once he's cooled down, and only avoids summary execution because Legio Invicta needs him, the sole surviving member of his Engine's original crew, to ease in the newbie replacements.
 * Unwitting Pawn:
 * Kalien is this to the conspirators.
 * , but that lethally backfires.
 * Well-Intentioned Extremist:  genuinely believes he's the doing the right thing by proving the Omnissiah and the God-Emperor are not one and the same, as opposed to   who's just making a power grab.