It SOUNDS like you're talking about the second one, correct? If so, then just simply go to the town like you normally do. (2) Friendly spy - on another quest, you're supposed to rendezvous with a spy who is supposed to give you some secret papers with information about the enemy, which you then bring back to the lord or king who assigned you the quest.
(1) Enemy spy - you're supposed to locate the traitor and follow him until he meets up with his handler, at which point you're supposed to arrest them both Wait, wait, there are two types of quests in the native game involving a spy:
