An attaché is an NPC you can attach to an army to provide the army with an additional special ability. When attached, the army it's attached to is considered its host, and the attaché moves wherever the army moves.
Attachés can detach from their host and move up to 2 hexes on their turn. Multiple attachés can occupy the same hex.
Enemy Armies & Attachés
When detached, an attaché is considered "wandering" and is vulnerable to being captured. If an army ends its turn on the same hex that the wandering attaché occupies, the attaché is considered captured by the enemy and its host becomes the enemy army. The attaché provides no benefit to the enemy army when captured. If the army an attaché is hosted by becomes disbanded, the attaché is considered captured by the enemy.
An army can only ever host 1 attaché.