Lysander: The Fist of Dorn (Black Library Advent Calendar 2013 #11)

Darnath Lysander is a man tortured by his past, a past in which the Iron Warriors play a prominent, and unpleasant, role. As the First Captain of the Imperial Fists must choose between the lives of innocents and the death of one of Perturabos sons, he recalls a similar incident that haunts him still, and must decide what mistakes are worth repeating. A Lords of the Space Marines short story by Anthony Reynolds