In Dominion: Alchemy, you can play Possession to "possess" the player to your left and effectively take over his next turn. What happens if he has a Possession in his hand, and you play it during that possessed turn?
Example
(Turn order is Alex, then Bob, then Carl)
Alex plays Possession.
He controls Bob's next turn, and plays a Possession from Bob's hand.
This means someone will possess Carl on the next turn - but is it Bob, or Alex?