This post will contain a lot of spoilers, so be careful. However if you play ATOS and stay stuck somewhere before a certain door, or miss an item such as a Black Die, you might be happy to find this walkthrough. Here we go!

After the first discussion, go talk with Lieutenant Big.
Leave for the room of the truck, and visit the small area at the bottom left.
Remember the colors on the floor, or write them down on a sheet of paper (or simply follow this walkthrough to the very end).

Go through the white door at the top of the room of the truck, and visit the small corridor. Check the shelves on the wall, and more specifically in the middle black square: you’ll find a black die.

Continue to the right, open the airlock and enter. Check the color symbols on the wall. Save them somewhere (in your brain, on a paper, or just keep reading this walkthrough)

Leave the airlock and check the digipad near the closed door. Try to find the code: you have to mix the colors you found near the truck, and in the airlock. It’s quite easy and you should quickly obtain the correct order for the code: 6234. So just press the 6th key (bottom right), the 2nd key, etc…

Take the ladder and visit the first floor to talk with Beck. At the crossroads, go to the left to find the hole of the relay station. Look at the text on the wall before you.

Leave this room and visit the terminal (PC room). Listen to Lantier and go downstairs with the ladder.

Put the Die in the teleport pod, and take the delivered key. Go use the key in the room with smoke: it needs to be updated. Go back to the terminal (PC room) and insert the key in the computer. You can now open the final door of this demo!