GoodReads Summary: Having recovered from his grievous injuries, Warmaster Horus leads the triumphant Imperial forces against the rebel world of Isstvan III. Though the rebels are swiftly crushed, Horus's treachery is finally revealed when the planet is razed by virus bombs and Space Marines turn on their battle-brothers in the most bitter struggle imaginable.
Not much an improvement from the previous books.
The plot could be seen from several books ago, so there is no big plot twist -- although one could say that there is one, a la George R. R. Martin ("oooohhhh, so edgy!"). But the general plot could be seen from the very start of the book, so there was no big surprise.
Also, some of very old clichés of every story are so used and abused that, when there is something "out of order" happening, you feel a bit like "yeah yeah, go on". There are no surprises, no twist that you can't predict pages ago.
And yet, there is one glaring plot hole that started in the previous book and still isn't explained: Why it happened? When did it happen?
Two books and no answer.
Also, the idea of ending blocks of text (think as subchapters inside the real chapters) all end in cliff-hangers, to the point that, when the story gets faster -- and the blocks smaller -- the amount of cliff-hangering is simply annoying.
On top of that, there is some weird character personalities changing from white to black -- which also happened in the previous book, but not with the intensity of what happened in this one -- that it feels more like a previous character just died and they put a new one with the same name.
The book got to the point that I almost relish on spoilers -- which I did look -- 'cause, honestly, I'm not sure I can stand so much of this thing.