So first up, this is available at GamesDay UK 2012. This first volume is titled "Betrayal" and I would guess its set on the initial purging of the Traitor Legions of their loyalist members on Istvaan.
Those images showed the following Legions in Heresy-Era garb:
-Sons of Horus
-Titan Legion (looks to be the Legio Mortis)
A MAP of the HERESY ERA GALAXY! ~Special note, I'm a giant map geek and had to research the locations of all the traitor legion homeworlds from scraps and quips scattered everywhere when we did our own Heresy Campaign book so many years ago. I'm super excited to see this all officially added to the fluff's canon.
My Death Guard are ready to roll! Who's onboard for Heresy-era gaming and modeling?