I'm of two minds about this book. On one hand, I really, really enjoyed this, especially in comparison with the first half of this duology, which I thought worked well UNTIL it became a unified story. This is obviously a novel, not a novella & some short stories put together, and that's a good thing. On the other hand, what I enjoyed MOST about this book was the first half, the kind of "setting all the pieces in order" and the tension and the character buildup. The second half, the huge four-sided, ever-changing battle, was far less interesting, and since it's HALF THE BOOK, it just kind of ... keeps going until it ends (and what the hell; I feel I missed the climax).
Ostensibly this follows another outing of the Lord Solar Macharius during the Gothic War. We've got human Imperial Navy folk upholding a shaky truce with a group of eldar against some Chaos baddies, but unbeknownst to them, there are some dark eldar lurking in the wings trying to make things go pear-shaped. Captain Semper, Horst - all your favorites are back! Plus approximately 7,000 new characters, from both the Imperial and the Chaos side of the fence.
I think the bit that was most shocking to me is this whole section that's very "feel-good," where Semper kind of shows up to the eldar & is like, 'We don't know enough about each other. Let's not fight!' and you think, oh, this is 40K; this won't end well. But then it DOES. In a damn-near "Lion's paw"-esque ending, the eldar come back in Semper's time of need & help him out of a bind. This is balanced with some of Maxim's horrific actions during the book, but still, it's quite shocking to see a 40K book with even that much sort of 'things work out in the end' to it.
Despite a third act that takes up over half the book, the climax is rushed & ... kind of confusing, but still I did enjoy it. I think Rennie is a good author, and I wish he'd done more 40K stuff. I think he improved at least threefold between the first book & this one. Oh well. Maybe one day.