I continue my reading of Horus Heresy series in disorder, but focusing mainly on Dark Angels-themed books (being my favourite chapter). My latest read, Angels of Caliban, has been a pleasant surprise.
In this volume we get to learn with lots of details mostly two plot lines: How began Caliban conversion to chaos, and how (and why) the Imperium Secundus and Triumvirate dissapeared. On one side, new details about Caliban hidden forces, about the origins of The Order, about how Luther slowly turns to rebellion after being banished to Caliban by the Lion. On the other, how the Triumvirate worked, with Sanguinius and Guilliman and the Lion who goes hunting for Curze with drastic measures. We also get to see more of the character of the Dark Angels primarch and some decisions that might have consequences...
There are also nice links with previous books, like the Tchulcha device the angels have, but also with future events, like mentioning Luther befriends Typhon (who is already tainted by Nurgle but keeps it in secret), of the old formations the chapter had (especially the Dreadwing), and we get to learn some "motivations" we can say of some of the will-be first Fallen Angels.
As a Dark Angels fan, can't but recommend reading it. There are some chapters who feel a bit long (e.g. a certain Luther speech...) but overall quite enjoyable.