You'll be up against a really flexible and challenging mission with Lady Boyle's party, but first you will have to do some interrogation work. Speak with the woman with the tweed cap, who will give you a key to an abandoned apartment across the street from the Hound's Pit. Check out the building now, because there's a Rune in it. Go to bed when you're ready to start up the mission. Head out and look for Sokolov in the locked cage by the water.

It's time to interrogate Sokolov. There are two ways to get the info out of him. First, you can release a pack of rabid rats on him, scaring him into spilling the beans. Then, there's the low chaos way of doing things, which entails bribing him with 150 coins worth of goods. If you're in a hurry or want to go high chaos, just release the rats. Otherwise, bribe Sokolov and enjoy the view of Callista in the bath afterwards. To do this, find Piero on the second floor of the Hound's Pit. He will be peeking in on Callista taking a bath. Offer to buy rare liquor from him for the 150 coins. Now you can bribe Sokolov. Speak with him after getting the info to get your target; you'll have to kill one of the three Boyle sisters, but your target will be randomized each time. That's because the party is a costume party, and the three Boyles will all be dressed the same. You'll have to figure out which one it is before killing them... unless you want to barge in and kill every single one of them like a madman, that is.

Before you head out, speak with Pendleton. He will have a letter for you to deliver to a man named Shaw, who will be outfitted in a wolf mask. Definitely don't agree to do this if you're going for the Clean Hands run, since it'll require that you kill someone in the end. Otherwise, go for it for sure.

Now it's time to head out on the mission proper. Check in with our next guide to figure out the best ways to get past the tallboys, and get away with the murder in the most clever and clean way possible. Or, you know... just kill everybody.