There's a war going on in skyrim yet they're are no specific intelligence agencies. For lore friendly purposes the modder would have to check for already existing imperial intelligence branches (if i'm not mistaken the blades were the former "spy" agents so I assume the penitus oculus has taken over that role). For the storm cloaks creativity is key go wild (the white hand, the snow blades, etc.) same premise as the imperials with the overall objective being to infiltrate the opposite factions court and feed key information to your perspective faction and even open the gate to the other key city (alternative ending to the war). If anyone's interested in working on this mod please contact me I have a lot of ideas (no modding experience) you can have the credit I just like having a diverse gaming experience.
