This page of the Baldur's Gate 3 guide has a walkthrough for Escape the Nautiloid quest. This walkthrough will help you complete the prologue.
- Find a way out of the Nautiloid;
- reach the bridge;
- connect the relay nerves.
This quest starts automatically at the beginning of the game. You are on the Nautiloid ship, and you are one of the survivors of the Mind Flayers' attack on Baldur's Gate.
As soon as you start (M1;1), head for the only accessible passage to the next room. From there, you can get out to the outer part of the ship. Before you do that, however, you should check out Myrnath (M1;1) located on the platform. You can reach him via an elevator (M1;2), which you can use thanks to the mechanism shown in the image below.
Interact with the man. If you successfully complete a skillcheck for strength, dexterity, or medicine (you need to roll enough points), you will remove the brain. If you succeed, you will learn that this is an Intellect Devourer - Us. If you agree, it will accompany you.
Then head to the outside of the ship. To get further you have to jump over a hole in the deck (M1;3). Going further you will encounter Lae'zel (M1;2). After a brief conversation, you will join forces to increase your chances of reaching the transponder and escaping.
A few moments later, you will have the first battle (M1;1). Your opponents will be 3 Imps. They move quickly and can deal damage from a distance. They're also resistant to fire, so if you are playing as a Wizard, deal them damage from cold.
After the fight, head to the stairs. You will be outside again (M1;4). The path leading further is to the right of them. There you will find another corridor (M1;5), which is blocked by a membrane. The only way to break it is to attack it.
This path will lead you to a room with capsules and a panel with three brains (M1;6). If you don't want to fight, don't touch the brain in the middle of the console. It will free prisoners who are hostile towards you.
Shadowheart is in one of the pods in this room. Unfortunately, all you can do now is try to get her released. However, it will not produce any results.
If you walk into the corridor to the right of the entrance, you will reach a path leading straight to the transponder. Use the recovery point (M1;8) to restore the health of the entire party.
When you enter the relay room, you will find Commander Zhalk (M1;2) fighting with a Mind Flayer (they are focused on each other, you can leave them alone) and a group of Imps. The game does not force you to fight them (however, you can gain additional experience points). You can simply go to the transponder and activate it.