Shunned by the rest of the Legions after the destruction of their home world, the Night Lords have fought without their disgraced primarch Konrad Curze for many years. But now the self-proclaimed ‘Night Haunter’ has returned and will lead them to the backwater world of Isstvan V, where a great treachery is unfolding, and the grim legionaries of First Claw will soon be forced to embrace their dark destiny.

It's the characters you know and (maybe) love from Aaron Dembski-Bowden's Night Lords trilogy, during the Horus Heresy.