The Trial of the Mantis Warriors (Legends of the Space Marines)

In the aftermath of the devastating Badab War, the Mantis Warriors Space Marines are put on trial. As he recounts the events that led his Chapter into treachery and then back to the Emperor's light, Chapter Master Neotera desperately tries to make his judges understand his innocence, even as he wonders if he and his warriors are truly guilty after all... Read it because
Chapter Master Neotera recounts the events that led his Chapter into heresy in the Badab War as the Mantis Warriors are put on trial for their very existence.