[Manuk]

I know that spyes have often improved stealth so they are harder to discover.
Also they have instill uprising order that creates unrest in the given province (their target is told by a message of this activity. Also computer players never use this option).
Also they revel more info of the province they are in (magic sites for instance).
If you are sieging a castle only a spy can tell who is inside.

The question is:

If you have a spy during a siege but you are neither the sieging or the sieged. Which info do you get? the sieging army?(most likely) or you get any info of the defenders inside the castle in this particular case.