Face Out of Sight
All on-guard cards are returned to owner's
hands. At the end of any turn, all wounded
agents and tapped agents are returned to
their owner's hand. Cannot be duplicated.

Does playing this card mean Agents played as Minion or Fallen Wizard characters to be returned to the hand too (since they are still Agents else you couldn't play cards like
Faithless Steward and long-event resources hit both players no matter of opposite alignment)?

What happens to the Allies, Items and followers such an Agent has got?

Is there any resource you can play to avoid this from happening, since this card is played in the long-event phase?
If this works, this card can be the killer card lurking in the sideboard to finish off your opponents companies one turn befor council (even worse than
A Malady Without Healing) because it is a resource card not a hazard you might be able to avoid or counter.