This guide details how to get the Elven ship, Lady Vengeance, sailing in Divinity: Original Sin 2 after escaping Fort Joy. The process involves a series of puzzles and interactions.
After removing your Source collar, your goal is to get the Lady Vengeance underway. This isn't done through conventional means; you must discover a unique method. Explore the ship, talk to NPCs, and gather clues. The key is accessing Magister Dallis' cabin and using the Ancient Empire Songbook.
Begin by searching the bodies of the magisters and ghouls on deck. A dead magister possesses a Sodden Diary containing a password for a stateroom door. You can also obtain the password via a skill check with the northern stateroom door. Additionally, you'll need a Strange Gem to interact with the Portside Stateroom door. A magic mirror (south of the stateroom doors) allows for respeccing characters and companions, useful for skill checks.
Using the password, enter the ship's quarters. Interact with the unconscious Bishop Alexander to find a Strange Gem within his regalia. Use this gem and the password from the diary to unlock the southern stateroom door. This leads to Magister Dallis' cabin. The cabin also contains a hidden hatch with ghouls and a Teleportation Prism.
Inside Dallis' cabin, talk to Tarquin and Dallis extensively. Locate the Ancient Empire Songbook on a pedestal. Reading it reveals the song needed to move the ship. It's advisable to speak to all NPCs before setting sail, as interactions will be unavailable once the ship departs.
Return to the deck and inform Malady about the songbook. She'll ask you to sing. Find the dragon figurine to the west of the deck and choose the option to sing the song. This will start the Lady Vengeance. Be prepared for a challenging battle with magisters immediately afterward; ensure your party is well-equipped.