First and Only by Dan Abnett

The provided text details a military science fiction narrative set in the grim dark future of the Sabbat Worlds campaign, where the Imperial Guard, supported by Adeptus Astartes and Mechanicus forces, battles the forces of Chaos. The story follows Commissar Ibram Gaunt and his Tanith First-and-Only regiment, known as Gaunt's Ghosts, as they navigate perilous combat zones, uncover a valuable Standard Template Constructor (STC), and contend with internal political machinations and personal betrayals. Key events include the liberation of Fortis Binary, a conflict on Pyrites involving infighting with the Jantine Patricians, and a climactic mission on Menazoid Epsilon to destroy the rediscovered STC against the wishes of powerful figures like Lord General Dravere and Inquisitor Heldane, who seek to exploit its potential. The narrative also includes flashbacks to Gaunt's early life and the loss of his homeworld, Tanith.