The Horus Heresy reading continues apace.
I am now on Corax, book 40, a collection of novellas and short stories about the Raven Guard and their primarch, Corvus Corax, all about the things they've been up to since their prior book Deliverance Lost. I've just begun this one.
Praetorian of Dorn, book 39, is set in the solar system, and an Alpha Legion plot there. As is usually the case with the Alpha Legion, it's not clear exactly what their objective is, other than speeding along the end of the Imperium and through that the extinguishing of Chaos through the same of humanity. This one has a pretty momentous ending, as Rogal Dorn, primarch of the VII legion Imperial Fists kills Alpharius, the primarch of the XX legion Alpha Legion. From here on, it's Omegon leading them as Alpharius, making a tragic mockery of their famous line "I am Alpharius." This is only the second primarch to die since the beginning of the series, and the first since book 5, Fulgrim (III legion Emperor's Children), where the titular primarch kills his brother Ferrus Manus (X legion Iron Hands) at the Dropsite Massacre.
Book 38, Angels of Caliban, seemed to bring a cap to the Imperium Secundus arc of the series, focusing on Macragge, where the primarchs Lion el'Jonson (I legion Dark Angels), Roboute Guilliman (XII legion Ultramarines), and Sanguinius (IX legion Blood Angels) try to maintain humanity's hold on the galaxy while fending of the destructive efforts of Konrad Curze (VIII legion Night Lords). On the other side of the galaxy, on Caliban, Luther turns his other exiled Dark Angels away from the Lion and back toward the ancient Order that ruled Caliban before the coming of the Emperor. There's trouble brewing, there.
Book 37, The Silent War, is a collection of short stories all about the various forces under Malcador the Sigillite, the Lord Regent of the Imperium. We see a lot of the Knights Errant, the beginnings of the Inquisition, and more interesting things kind of behind the scenes of the galactic civil war.
The Path of Heaven, book 36, brings the White Scars home to Terra after years of harrying Horus' various forces on the edges of the galaxy. The Emperor's Children and the Death Guard figure into the story here, and Leman Russ (VI legion Space Wolves) makes an appearance toward the end, as well, as Jaghatai Khan (V legion White Scars) faces him to apologize for leaving his brother in a lurch back at the Alaxxes nebula, where the Wolves were beset by the Alpha Legion. Now that the Khan has returned, there is work to do reinforcing the Terra's defenses. The traitor legions are on their way.