Black Oculus: The Horus Heresy Series (Unabridged‪)‬

After Fulgrim's ascension to daemonhood at Iydris, Perturabo and his Legion were trapped by the singularity at the heart of the so-called 'Eye of Terror'.

Their only option? To thread the needle, and dive into the heart of the black hole. Perhaps by sheer blind luck, they were transported far across the warp to the Tallarn System but the Navigators in service to the Iron Warriors fleet were irreversibly corrupted by that harrowing experience. Now they serve a new purpose, and Perturabo's plans for revenge come closer to fruition....