Hmmm.  Making me think about it again.  Steampunk isn't really my thing.  If it had been written by another author, I never would have given it a thought in the first place.  And I'm not really in a good head space right now to start something new.  But I loved Codex Alera, so that's a little tip to the scales in favor.

I don't really see the steam punk in Cinder Spires at all the be honest.  It's just.... British.

Something else to consider that supports the Baynard theory; The attack on Baynard and Grimm near the beginning of the book.  Why would the Silkweavers attack them and potentially blow the Aurorians cover?  Why were they in Hobble Morning, hundreds of miles above Habble Landing?  Was Cavendash trying to take out Baynard (her spy) before he could be compromised?  It's not like she had a reason to be wary of Grimm yet.  She seems like the kind of gal to keep her puppets on a tight leash. 

The only thing that makes me not want to finger Baynard as the spy is that Fenrus seems to trust him.

My theory is that whatever attacked Baynard and Grim in the tunnels wasn't actually Silkweavers but something else and now Grim has some kind of important hoodoo running through his arm.