Before we consider anything else, we should state the obvious: this was always the nightmare brief. Dan Abnett's job was to take the noble and certain Horus and take him places where his self-doubt would blossom to the point where it was a real problem. Ben Counter got to pick up a Warmaster already fully devoted to overthrowing his father and explore the Faustian deal Horus makes as part of his upcoming campaign of destruction. Graham McNeill, on the other hand, had to start off with a shaken and uncertain but still resolutely loyal Horus, and conclude with a Primarch not only committed to betraying every principle he once held dear, but willing to kill his own men and his own brothers to do it.
That is not an easy ask, especially in the frame of four hundred or so pages which are also supposed to contain a healthy dollop of the military action expected of the Black Library. It was always pretty much inevitable that McNeill would fail, which makes picking at the reasons why the book did indeed fail to deliver feel a little unfair. The chasm between Abnett-Horus and Counter-Horus was always going to be simply too wide to jump in a single book.
Nevertheless, it's worth sifting through the rubble here, if only to determine which strands of the story brought the book closest to succeeding. There is certainly at least a partial defence that can be mounted. One of the major criticisms of Horus in the book is just how stupidly he seems to be acting. He falls completely for Erebus' routine on Davin, despite it being so transparent that even a man more interested in ogling women and dreaming of fermented yak's milk can work out something is amiss. He charges into the ruin of Temba's flagship despite it being an obvious act of tactical idiocy. He completely swallows Erebus' claims of the Emperor's desire for godhood based on two visions granted to him by "Sejanus", even after it's revealed that his dead friend is really Erebus, a man who goaded Horus into the duel that almost killed him, that has now been revealed as a sorcerer in direct defiance of Imperial Law, and who most pertinently has demonstrated he can make Horus see things which are not real.
Given all this is is tempting to write the story off as being of the kind where the protagonists are required to be utterly stupid at key moments so that the plot can unfold with less effort from the writer. And whilst it's true that this is not a curse the book escapes entirely - not just regarding Horus; Loken and Torgaddon begin here their campaign of ridiculous passive idiocy which will grow to unbearable levels as Galaxy in Flames progresses - there is an underlying logic to Horus' foolishness. Loken views it as a desperate fury borne of the insult Temba has laid against him, but as an explanation this starts off unconvincing, and collapses into complete irrelevance by the time Temba is killed. Far more likely than this being a case of wounded pride is that the problem stems from Horus trying to outrun the avalanche of doubts set in motion by his failure with the interex. The Warmaster comes across as a man desperately afraid of reflection (it's surely a coincidence that the repeated theme of reflections from the previous book has completely disappeared here, but it's a happy one), barrelling through life specifically to stop himself pondering just how badly things seem to have ended up. And of course when you treat life that way, you end up making new and greater mistakes, which means you have to run even harder to leave them behind.
Viewed this way, we see Horus not as a petulant man taking any opportunity to lash out at those he deems to have wronged him - or at least, we see him as not entirely that. From this angle, the decision to believe Erebus' ridiculous claims makes a certain kind of sense; if the Emperor's goals were always vainglorious and self-centered, there is no reason for Horus to feel bad about anything he has done wrong. This possibility offers him the opportunity to short-circuit the building crisis that has been pressing at his back for months now; of course he takes it. The shouting match between Magnus and Erebus over Horus' responsibilities is therefore spectacularly beside the point. The true choice for the guy actually caught in the middle isn't about his loyalties, it's whether he can admit he's allowed himself to fail so completely at living up to the standards he set himself.
And as it turns out, he isn't. He transfers wholesale the blame for his catastrophes (as he sees them) to the Emperor, and history is written. But if that sounds like a way to offer False Gods a blanket pardon for its problems, then believe me it isn't. Because the real flaw in the book was never the logic that led to Horus turning from the Emperor. It was the secondary decision to enact that turn through sorcery, assassination and planning massacres of his former friends. There's just no way to square that circle, not inside four chapters.
Which means that the final section of False Gods is a difficult to swallow. Add in a first section that's rather understated, and the novel demonstrates deep structural problems. We can, as seen above, construct a redemptionist reading of part three, but said reading requires a pushing of a subtext that at least partially reduces the rest of the section essentially meaningless; three men discussing a decision already made for reasons none of them have grasped. Really, if anything can be said to be the book's saving grace, it's its second section, "Plague Moon". Here, at least, McNeill brings his A-game. The problem of the headstrong Horus is still evident, but with his ardour up and battle at hand we need no potentially tendentious reading to understand his carelessness. Moreover, the actual battle of the swamp is well-realised; the stinking, foetid waters of Davin's moon and the horrors that dwell within being both nicely described and contrasting well with the freshly-painted austerity of the Sons of Horus and the crumbling majesty of the Glory of Terra.
But it's not just the crafting of these scenes of struggle that make the section relevant. The choice of Nurgle as the corrupter of Temba is clever one. It links together the image of the rusting hull of Temba's flagship, the pathogen that begins to eat Horus from the inside once unleashed by the anathame, but more importantly it reminds us of the metaphor of heresy and betrayal as diseases spreading from mind to mind. This is a metaphor used frequently both in general and by Games Workshop specifically, so the association here makes complete sense. It also provides us with what it possibly the only way to view the events of the novel's final chapters as a logical development from earlier chapters. If heresy really is a sickness, then is it at all a wonder that the virus Horus has contracted has damaged his mind somehow, causing him to see horrifically violent solutions as obvious approaches, where once he saw them only as admissions of failure.
Well, maybe. But such a solution does far more harm than good. On the sheer level of plot mechanics the idea that Horus becomes the crazed dictator shown in Galaxy in Flames because he's been infected is rather narratively uninteresting; once we remove Horus free will in such a way we reduce the flawed but noble warrior of Horus Rising into little more than sneering MacGuffin. Writing off "Crusade's End" as a brief but significant misstep might actually be preferable in terms of salvaging the trilogy as a whole. More importantly, though, the disease metaphor carries with it some exceptionally unpleasant connotations. It simultaneously robs Horus of moral responsibility for the decion on which the entire series is based, and equates disagreement with authority with a form of sickness. There's nothing wrong with presenting the Imperium as viewing heresy that way (so long as it doesn't appear the author is buying into that idea), but as far as actual real-life people are concerned, this idea should be rejected with all possible force. New ideas and principles can spread like a disease, but there we must abandon the metaphor, or else commit ourselves to a form of authoritarianism no less unpleasant than that of the Imperium.
What all this amounts to is simple; we can all choose for ourselves how close McNeill's novel comes to performing it's nigh-impossible task. But in doing so we should be aware that a balance is in play. The closer we come to signing off on Horus' betrayal as plausibly tumbling from the seismic shifts of earlier events, the harder we have to push theories that either lessen the impact of those events, or which come altogether too close to embracing the kind of thinking which makes the background of this fictional world as dark and oppressive as it is.
So a strong effort doomed to failure? Or a coherent tale of treachery underpinned by worryingly retrograde politics? Either way, False Gods gets the same score.