Inferno! Vol.2's The Thirteenth Psalm is today's Monday short from Black Library, so it is now available individually, at least digitally.
If you've been on the fence about getting Inferno! for one story, this is your time. It is freakin' brilliant.
Do you know where it fits, story wise?
The Thirteenth Psalm comes after Requiem Infernal, using Athanasius' chronology to date it.