CL Werner’s Iron Devil is an Astra Militarum story which was first released as an audio drama before then being revised and expanded into a prose story. The Cadian 267th are embattled against orks on the ravaged planet Sanzu, but find themselves exchanging one danger for another when they’re forced to seek shelter from the planet’s toxic weather. Trekking their way through dangerous territory to a vast, crumbling Adeptus Mechanicus facility, the few remaining Cadians hope to find shelter and supplies, but there’s something large and angry waiting for them in the shadowed halls of the manufactorum.
It’s billed as a 40k haunted house story, and that’s sort of accurate; the Cadians do spend some time exploring and falling victim to the dangers of a shadowed, echoing building, while the entire planet could arguably be considered out to get them. For all that, however, it’s actually quite a conventional Imperial Guard story, with a fairly straightforward plot, characters who are fun but not particularly developed, and a protagonist that’s rather spoilered by the cover art. There’s plenty of plucky heroism from the Guard, and it’s hard not to enjoy greenskins chanting “Morka-morka-morka!” as they fight, while overall it’s entertaining enough without really excelling.