Playing Seventh Level and have Book of Mazarbul attached to a hero. It is listed as "item.artifact." and "objective".

I just put the Unexpected Courage attachment on another hero.

When questing, the revealed card was a treachery that said "Then the last player discards an attachment he controls".

Can I discard Book of Marzarbul back into the staging area instead of discarding Unexpected Courage? The book is an "objective" card but is attached to a hero....

Thanks!

You can discard it for these two reasons combined and due to the text on Book of Marzarbul it would return to the staging area:

(1.07) Control of Objective Cards

When a player claims an objective card, he gains control of that card unless otherwise directed by a card effect.

(1.23) Attachments

Any objective card that attaches to another card is treated as an attachment in addition to its other card types.

Thanks!!