Helsreach is the second novel in the Space Marine Battles Series. It was written by Aaron Dembski-Bowden and published in 2010. It was republished in the Armageddon (Anthology) along side Blood and Fire (Novella) in 2013.
Set during the Third War for Armageddon, Helsreach follows Grimaldus, the newly promoted Reclusiarch of the Black Templars. Leading a group of Black Templars, and supported by the 101st Armageddon Steel Legion and Titans of Legio Invigilata, he is tasked with the defense of Hive Helsreach from the Ork invasion.
The subplot involves a Black Templars Techmarine as he attempts to gain access to and activate Ordinatus Armageddon for use in defense of the hive.