On the world of Phaedra, a force of skitarii - the front-line soldiers of the Adeptus Mechanicus - embark upon a dangerous to assault a stronghold of the xenos tau and recover a priority asset for their tech-priest master, Magos Caul. As they face the diminutive drones and hulking battlesuits of their alien foes in the jungles of the Dolorosa Coil, their target draws nearer. But just what is Objective Skysight, and why is it so important to the tech-priest? Read it because Ancient clashes with the cutting-edge as the Omnissiah's holy technology combats the soulless heathen tau. And a secret objective leads to more than the lead character, tech-priest Magos Caul, could ever have bargained for.