The rules say that during set up you are to, shuffle your detective's Light cards and draw two, and shuffle your Dark cards and place them on the board.

Now, does that mean ONLY the light/dark cards for the plot that you have drawn previously? Or all your light/dark cards, irrespective of plot?

All of 'em. Any of your twilight cards can happen, regardless of plot (but the in-plot cards are slightly easier to play, due to the twilight cost modifier).

Ok, thanks.

I guess I just wanted them to be plot specific, as it would limit the amount avalible and see a sharp increase in the "theme" feel of the game? I don't kow… but having all of them does give more options.