Promotional fiction piece that provides background information for Rogue Trader.
From the introduction:
"Ah, so you wish to know of the Koronus Expanse—that the Mechanicus Calixis sometimes still call the Khronus Expanse after he who was said to be its original discoverer. I know of a man you should listen to, though his sanity wanes in these late years, and his tractability with it. He is a holy man born of Archaos and at one time a chronicler for the Rogue Trader Amphian Deed, yet somehow evaded the pyre that was Deed’s recent end."