various
The Imperial Truth

The Emperor decreed long ago that there were no gods upon the Earth or in the sky, and that all of mankind's belief and aspirations should be poured into His vision for the galaxy instead. Upon such unshakeable foundations was the Imperium to be built - except that the Imperial Truth was a lie.
The Horus Heresy
collection

It contains:
Hands of the Emperor
By the Lion's Command
The Phoenician
The Devine Adoratrice
Lord of the Red Sands
All That Remains