Like the White Scars and the Iron Hands, the Raven Guard are one of those Space Marine legions that just never seemed to get much in the way of publicity. Sure, each of them have a single special character in Codex: Space Marines, and there's the odd book devoted to them or their successor chapters, but it's pretty small potatoes for a First Founding legion. The Raven Guard are third tier, falling behind not just the big names, the Ultramarines and Blood Angels and Space Wolves, but the lesser-known but codex-toting Marines, the Black Templars and the Dark Angels. Which is all a really long-winded way of saying that unlike The First Heretic and A Thousand Sons, I went into Deliverance lost with no real preconceived notions one way or the other.
Deliverance Lost picks up from the infamous Dropsite Massacre, which at this point is probably running just behind D-Day for 'most fictionally covered battle', where the Raven Guard have been practically destroyed. Corax and a handful of his men make it off the planet, thanks to a slightly psychic noble and a rather daring Raven Guard strike cruiser commander, and the primarch of the Raven Guard is faced with the fact that there's no real way for the shattered remnants of his legion to participate in the accelerating civil war. The Raven Guard would make a particularly strong chapter, but this is the time of the legions, and there just aren't enough of them left for that sort of designation. Which is why Corax decides to take drastic measures to rebuild his legion, setting the plot of the novel into motion.
It's a bit of a slow burn, really, but Gav Thorpe puts the downtime in the middle of the novel to good use. Corax, of course, needs to be built up; unlike Magnus the Red or Leman Russ or Roboute Guilliman, this is not a primarch the reader can be expected to know from the start. Humorously, the only think Corax is really famous for are his reputed last words, which are not going to be of great use in any story but his very last. Thorpe unspools Corax' past through a series of flashbacks, explaining how he came to be on Deliverance, his campaign to establish himself as ruler and his meeting with the Emperor, the seminal events in every primarch's pre-Great Crusade life. But he also spends time on a couple of Raven Guard characters, who give the reader a good sense of what it means to be a member of this particular legion, demonstrating both their common cause with the other legions and the particulars that make them unique. And even with all that, there's still a little time left over for an Alpha Legion character or two.
I've said it before, and my opinion hasn't changed; I fundamentally do not like the way the Alpha Legion decided to align with Horus. The Emperor's goal with the Great Crusade was always and explicitly to elevate humanity to the rulers of the galaxy, so to have Alpharius and Omegon swayed by a group of aliens explaining how the extinction of humanity would destroy the powers of Chaos just rings false. Not only does it not really make sense, since Chaos pre-dates humanity and Slaanesh was explicitly born from alien actions, with no human involvement whatsoever, but it requires the twin primarchs to somehow intuit that while what the Emperor has always said he wanted was the primacy of humanity, secretly what he wants even more is the destruction of Chaos. Also, they have to trust aliens, which is sort of a non-starter in the grim darkness of the far future. I just don't buy it.
That being said, though, Thorpe does a good job with the Alpha Legion characters. The soldiers are believably conflicted about their actions, infiltrating and sabotaging a loyal legion, killing their battle-brothers while pretending to fight alongside them, and Alpharius and Omegon both get some good scenes. The former's meetings with Horus, which book-end the novel, are particularly solid, presenting Alpharius as a consummate schemer faced with an ego-maniacal madman in Horus, both of them entirely aware of the others fundamentally untrustworthy nature. Given that the traitor primarchs as basically a collection of unbridled egos just waiting to stab each other in the back and festering grudges that have completely ruined the ability to think rationally, this is about what I would assume every gathering of more than one of them would boil down to. Also, there's a nice little Fabius Bile cameo in the end, which ties smoothly into his codex abilities. It's really quite delightful, and clear evidence of the author really thinking out how to connect fluff and tabletop.
Deliverance Lost is another of those 'basically inconsequential' Horus Heresy novels, which is to say that by the time the story is resolved the situation is basically back to where it started. Like Nemesis and Battle for the Abyss, however, Deliverance Lost manages to be an excellent read despite not really advancing the larger story of the Horus Heresy, and like those others it also manages to plant a few little seeds that will, a few books down the line, no doubt pay off nicely.