Sammael: Lord of the Eternal Hunt (Black Library Advent Calendar 2013 #24)

Supporting the White Scars on Gehft, Sammael, Master of the Ravenwing, prepares to aid Korsarro Khan against the plague-ridden warriors of Chaos. But when an ancient secret is revealed, Sammael must choose between the bonds of brotherhood and pursuit of the oldest foe of his Chapter. A Lords of the Space Marines short story by Ben Counter