Steve Jackson, Is That You?
This is a playthrough of A Stony Sleep from The Emperor Protects, so be careful not to let on to your GM that you listened to it. It does reveal one crucial plot event, and foreknowledge will inevitably affect the way you play this scenario. As always, be aware that the podcast is not really family-friendly, if that sort of thing bothers you.
Some episodes feature bonus material after the closing music, of varying interest. This is usually either teasers, or conversations that were sort of interesting, but not a bit tangential to the main episode.
You would not believe how much crisp-excision this podcast required. This was actually one of the main reasons I didn't get round to doing it sooner. I'm not sure if you can tell, but there are a few sections where I had to remove entire conversation threads because crucial parts were obscured by unbearable crunching and/or rustling. There was a certain amount of careful doctoring, including pasting in alternative versions of a word from elsewhere in the recording to create a clean sentence break.
I should point out, though, that I have in no cases changed the actual meaning of what was said! Just tidied up bits where I had to chop off a run-on sentence or a bit where we talked over each other and led into another conversation that couldn't be rescued. Nothing crucial was lost, but the podcast is quite a bit shorter as a result. The surviving crispy sections should give you a clue just how bad the excised bits were.
This is an occupational hazard of actual plays - very few snacks are silent and gaming is a snacky sort of hobby. More recently we've been putting things in bowls before recording, which helps, but I'm not sure how the squeaky-clean podcasts tend to manage. Unless they just don't eat, and are tireless robot gamers. Always a possibility.
I Fought The Lore
When we learn about the "other Astartes", it's obvious to me and Dan (with our extensive 40K background) that this will be the Alpha Legion. However, it's not clear whether our characters are allowed to know that. This is one of the points where establishing exactly what canonical knowledge is widespread, what is secret, and where different kinds of security clearance fall is really difficult in this game.
One of the reasons for this is, of course, that the 40K universe has been built up over decades by a whole load of different writers and gone through several major editions, each with their own angle on the truth of the situation. It's not clear how much access ordinary space marines have to Chaos-related information, and what is strictly inquisitorial or known to more senior marines. The RPG in general isn't especially helpful about this, and knowledge is absolutely one of the areas where I'd really have liked them to lay down some suggested difficulty guidelines, because this stuff is not remotely obvious. It's even worse once you start to move into things that aren't massive and well-established parts of the game canon (like major Chaos Space Marine legions) and into some of the crannies, like Imperial Navy lore or even psyker lore.
Broadly speaking, you have to assume that all space marines know about the existence of Chaos marines and renegades, and therefore at least a basic amount about Chaos. For a purely practical standpoint they must, must also be taught the tactics, equipment and abilities of Chaos marines, because the entire point of the Astartes is to fight the enemies of mankind, and refusing to teach them anything about fighting the one threat that did come close to wiping out the Imperium would be too stupid even for the Imperium. So if they know World Eaters are involved in a situation, there is no question in my mind that they should understand this will mean Khorne berzerkers, and therefore terrifying melée specialists, as well as a focus on mass slaughter of everyone possible, which will likely result in demons appearing who are also melée specialists. If they know Tzeentchian marines are involved, they should know to expect vile sorcery, a focus on ranged weaponry and maddening, fast-moving demons that spit flames and lightning.
It's less clear how much this extends to more strategic considerations, since it's generally senior marines who will be taking strategic decisions anyway. Do the ordinary marines need to know the typical signs of Alpha Legion operation, which are extensive use of cults, sabotage and misinformation? Do they need to understand that Slaanesh worshippers will aim to take captives for hedonistic rituals, offering certain strategic opportunities and informing loyalists about their likely movements? It all depends very much on how you view the information structures and trust within a chapter, which varies by chapter, as well as how you perceive the role of space marines in the Imperium as a whole. If they are basically soldiers, this kind of information is less important and might well be kept secret by paranoid officials. If they have a wider remit that includes investigation, small-unit missions and acting as aides or advisors, then it doesn't really make sense to me for them not to have that kind of information. Sending in a small unit to investigate situations when they aren't given enough information to analyse, identify and countermand threats is not sensible.
All this is a very long way of saying that I feel like this is a situation where the Fists should just have got the information. This isn't particularly complicated stuff: this is Traitor Legions 101. I have no idea what the actual mission stated, but the rulebook gives no guidance on how to handle this, and so I don't think Arthur's to blame. From what I've seen, any notes in the mission most likely offered a -20 penalty to Forbidden Lore rolls on the basis that you're trying to use Forbidden Lore.
Slightly later on, our in-character knowledge includes detailed understanding of the mindset of the Alpha Legion. I'm not trying to pick on Arthur here, not least because he used this on the spot as a way to give us metagame knowledge ("step away from the massive paranoia tangent of obsessing about this detail") without flat-out telling us in GM-voice that it's a result of scenario design clashing with reality. It seems perfectly reasonable that we would Know Our Enemies, and it's certainly plausible that we'd have memorised specific stuff about each legion without necessarily wanting to positively identify a specific group of enemies based on some general clues. I'm partly just flagging this up in case anyone else spots it, and partly because the contrast between these two situations just further emphasises for me how unclear the books are on this aspect of the game.
Of course, it's possible one reason the rules are pretty general about knowledge is that it's taken from a ruleset designed for all possible (okay, likely) 40K characters, and "common knowledge" varies massively by role in the universe. At the same time, this strikes me as exactly what individual books are for in such a game line. The summary for Forbidden Lore: Traitor Legions is just a few words, and it contrasts significantly with that for Common Lore: Adeptus Astartes and indeed Forbidden Lore: Adeptus Astartes.
Forbidden Lore: The Traitor Legions: The secrets of the lost Space Marine Legions, their names, and the sad tale of their fall from grace.
Forbidden Lore: Adeptus Astartes: Extensive knowledge of the practices, organisation, and homeworlds of the Imperial Space Marines and their Chapters, including hints and rumours of their myriad of secret rituals and methods of recruitment and training.
Common Lore: Adeptus Astartes: An understanding of the role, function, and nature of the famed Imperial Space Marines, as well as a knowledge of the commonly known Chapters and their practices and areas of operation.
Note that CLAA specifically mentions the practices of Chapters, and FLAA specifies their practices, rituals, methods and training. FLTL is far more cagey about what is actually included, more or less leaving this up to the GM. I find this unsatisfactory.