Lysander: The Fist of Dorn(2013)

Andy Smillie

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 Perturabo’s sons, he recalls a similar incident that haunts him still, and must decide what mistakes are worth repeating.

Read it because
A Lords of the Space Marines short story by Anthony Reynolds