So, on this very first screen, I have to walk into the tower in order tomeet the Masters (I guess).
I tried to enter the open door many times (clicking, using arrows) with no effect.

Also, I don't find any button to quit the game (escape does not work) or to go back to the main menu.

Any clues welcome :p

You should only need to click the HAND icon (or verb coin button) on the door, and D'arc should open it and walk in.

Is that not what's happening for you? How about if you restart the game?

If it's a real issue, I'd need a savegame in order to investigate it.

OK, not sure if it is an issue or just me missing obvious things, but I restarted the game and activated the dropdown buttons bar in the controls settings. It's OK now, I eventually managed to enter the Tower.

Thanks for the reply !

Haha. I had the same problem. I clicked dozens of times with the walk symbol on the door - nothing happens... Why I should use the hand symbol on an opened door? If the logic is the same in the rest of the game, then I see black for my success... ;-)