This was announced in the latest UK White Dwarf.
Czevak's been a GW metaplot device for 40k for some time. He seems to have a complex relationship with the Eldar, and to spend a lot of his time being chased around by Ahriman, perhaps because he's one of the few humans who knows the location of/has visited/ the actual Black Library, the Eldar's repository of all forbidden knowledge.
It'll be interesting to see how this one pans out, and nice to have another novel series starring a named Inquisitor to add to the Draco, Eisenhorn and Ravenor series'.
Despite this it is still grimdark.