WARNING SPOILERS START HERE.
The concept of "The Mark" and in this case, the Mark of Calth, as a timeline of events preceding and encompassing an event was pretty cool and a very good way to showcase the precise and measured way of war that the Ultramarines wage. Furthermore, this "Theoretical" vs "Practical" that the Ultramarines keep talking about is very characterful for Guilliman's legion and really defines the Ultramarines in a way the Codex and the Uriel Ventris series by McNeill never did but always should have. The Ultramarines are portrayed as the Masters of War that they are, but without being the emotionless Codex following automatons that people often mistake them for. There is alot of character and diversity presented, and how they face the adversity they are presented with in a calculated yet highly emotional manner is very refreshing.As far as action goes, Dan proves once again he is a master of war. He would have been a great student of Sun Tzu, or at least a great advisor to Spielberg and other movie makers. My favourite part is actually the start of the calamity. What the Word Bearers did is genius, and giving credit where credit is due, Lorgar isn't the mastermind here, Dan Abnett is. I really loved how it started with the minor boarding of the Campanile and you don't know where it is going to go from there, especially with the massive defense grid around Calth. But then he goes through the destruction of the ship and the grid in one of the coolest sequences in Black Library history and you can just see it all unfold even though it is happening in the smallest fraction of a second.
This book didn't develop the story of the Heresy too much, but I do like how it details the interpersonal relationships of the Primarchs more, particularly when it discusses in details the strengths and weaknesses of each one and how Guilliman maintains that any war could be won if he had Sanguinius, Ferrus Manus, Russ or Rogal Dorn, the "indomitable few" as it were. The novel also juxtaposes the Ultramarine view of the Word Bearers against what was presented in The First Heretic by Dembski-Bowden in a very good way.
Where the questions are left lingering though is surrounding John Grammaticus, Oll Persson and the Emperor. I think I have figured it out though. There is clearly only one answer. They are immortals.
I guess this is why Horus will go for the Emperor's throat, the only way to kill him is to cut off his head with a sword. Joking aside I really can't wait to see where this all ties together.
But really what is with these guys? Where did they come from? Who are they? But it is nice to see more of the Cabal come into play, especially so shortly after the roll they had in Deliverance Lost, with Legion being the first and last time we had seen them before that. I am however waiting for Eldrad Ulthran to step in more and play a big roll here. He is part of the Cabal and we all want to see him "be a Dick".
All in all I give Know No Fear 5 out of 5 Aquillas. Probably the best Ultramarines novel around, and does them much better justice during the Heresy than Ben Counter gave them in Battle For the Abyss.