Piero is not availible for this mission. His door will be locked. It says he is upstaris, but he is no where to be found.
Just talk to Samuel again and head to the party.
You can choose to stealth your way in or just "crash" the party like you never crashed one before. Since I was chaos, I crashed the party. Tallboys are a problem, but they can be dodged with blink, shot, or shot in the back where there fuel tanks are.
Once inside the party your just going to have to assasinate lady boyle. Although there are THREE lady boyles.
You can assasinate them all to make things easier.
Then make your way back to samuel,there will be another tallboy outside though, so either take him out or blink your way past him to the boat.