Above the Sorrows
"When revealed, discard the top card of each opponent's deck. Then, if this is your revealed plot card, trigger the "when revealed" effect of the top River plot card in your used pile."
At the Palace of Sorrows
"When revealed, each player chooses a card in play which he or she controls and puts the chosen card on top of its owner's deck. Then, if this is your revealed plot card, trigger the "when revealed" effect of the top River plot card in your used pile."
So over the weekend I learned something new while playing John Bruno (mathlete) and I wanted to bring it here so people understand the the ruling. Maybe I am the only person that was getting it wrong.
The way I was playing it was when I revealed At the Palace of Sorrows I would have my opponents choose a card in play to place on top of their deck, including myself, then have my opponent discard it to trigger the Above the Sorrows plot effect.
I was told / we examined the frame action windows and as you can see the "morribound" card does not get place on top of the deck till Step 6, after the action of discarding the top card of your deck.
I was little frustrated by that but I guess I understand now. I guess I was treating as the following:
At the Palace of Sorrows
"When revealed, each player chooses a card in play which he or she controls and puts the chosen card on top of its owner's deck."
This is the plot phase effect that must be fulfilled.
Then, if this is your revealed plot card, trigger the "when revealed" effect of the top River plot card in your used pile."
This is a separate plot phase effect that has its own action windows.
Thanks John for showing me the ruling.