All right, now I'm wondering - what exactly is the difference between plot difficulties in the original System Shock? I'm pretty sure that the lowest difficulty just removes all plot-related locked doors etc. and allows you to roam the station freely, whereas the highest difficulty retains all plot elements and adds time limit. So what exactly is the difference between the 1 and 2 settings?

One walkthrough I found said this:

"MISSION = 3: You have 7 hours to beat the game (good luck, you'll need it). On any other setting, there is no time limit."

The hintbook in the extras details all the differences.

Essentially the main difference between 0 and 1 is that 1 has logs while 0 has none at all.
2 adds access cards/locked doors and SHODAN has a security level you need to reduce
3 adds a time limit

Oh okay, I guess what I have searched for has been with the game all along. Oh well. Thank you for responding.