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 an unconventional method. Explore the ship, interact with NPCs, and gather clues. The key is gaining access to Magister Dallis' cabin and the Ancient Empire Songbook within.
Begin by searching the bodies of the magisters and gheists on deck. A dead magister holds a Sodden Diary containing a password. You can also obtain the password by successfully completing a skill check with the northern Stateroom door. You'll also need a Strange Gem, found later, to interact with the Portside Stateroom door. A magic mirror nearby allows for respeccing your party.
Using the password from the diary (or skill check), access the ship's quarters. Interact with the unconscious Bishop Alexander to find a Strange Gem. Use this gem on the southern Stateroom door, then use the password to unlock Magister Dallis' cabin. This cabin also contains a hidden hatch with gheists and a Teleportation Prism.
Inside Dallis' cabin, talk to Tarquin and Dallis. 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 proceeding, as interactions become unavailable once the ship sails.
Return to the deck and tell Malady about the songbook. She'll ask you to sing to the ship. Find the dragon figurine to the west and choose the option to sing. The Lady Vengeance will begin to move. Be prepared for a challenging battle with magisters immediately afterward. Ensure your party is adequately prepared.