In my idea espionage system consist of following things:


Spy unit: These units main work is to setup spy post(nodes) which cannot be seen on map. It can be discovered by spy operation.


Nodes: the nodes are place where player can initiate spy operations and also help to spread spy web.


These are of two types:


Main node(red dot)

Spy post(black dot)


Main node(red dots): These are built by making intelligence district which can be built 1 per territory. 


It can initialize spy operations.

It can only defend territory against foreign spy operation and can involve other main node and even spy post to eliminate foreign spy web.


 Here blue dot is making spy web to detect foreign spy web to destroy it.


Spy web can be destroyed by destroying spy post( black dot). These are hidden to find them spy operation should be started.


In defence operation we can involve more than one main nodes but will stop other operations which main nodes were doing.


Spy post(black dots): These can only be built by spy units. These can help player to target other players by spy operations.  These spy post have communication range means that each  spy post should be in an adjacent territory. If one of them got destroyed will cause communication blackout.

In it map main node(red dot) is performing spy operation in foreign territory with help of spy post(black dots).


Each spy post can only perform one operation.


More than 1 spy post can be used for spy operation for greater impact like:


Misinformation campaign: The spy post involve in the operation will cause stability penalty.


Proxy war: the spy camp involve in operation will act as rebel camp. The rebels will spawn from these spy camps.


There can also be intelligence sharing agreement which will able to see hidden spy web of that civ and player can use spy web and can also use spy post.