After a cutscene you find yourself dressed up, in a coach to the party. You will be without weapons of course, so this mission will be entirely stealth and social interactions. Follow the butler Luca through the mansion. Bill and Hosea will split off to join the party while Arthur and Dutch head upstairs to speak with Bronte.
After greeting you, Bronte will point out several of the important personalities at the party then give you leave. Dutch and Arthur join up with Bill and Hosea, and you all split up to mingle at the party. Take note of the location of the mayor by the fountain.
Avoid this location until you have the first gold medal requirement. Shortly thereafter the fireworks show will begin, and the mayor will get a message from none other than Leviticus Cornwall! When you reach the bottom of the garden stairs, wait for the servant to go inside and the guard to go to the south, then follow the servant.
When the servant goes into the next room, go through the door to the north and wait by the door while they talk. Wait for the maid to go through the door to the west, and the servant to head for the stairs.
Quietly follow him. Wait until the servant goes into the next room to the south, then go into the room and inspect the ledger. Turn around and go back out the way you came, returning to Dutch on the balcony overlooking the party. Bill and Hosea will show up a moment later, and will proceed to exit the party.
