Looking Glass Studios released the sequel to Thief in 2000. Utilizing the same DARK engine that powered the original Thief, Thief II had an almost identical look and feel, with only minor graphical and programming improvements. The basic gameplay was also fundamentally similar to the original Thief, but many new elements had been added, including technological gadgets such as a remote eye camera. Other changes include an increase in the number of A.I. behaviors, and the addition of female guards and soldiers. Responding to criticisms of the original Thief, the missions in Thief II were designed much more around typical thief-like behavior, and much of the game is spent robbing the rich denizens of the City rather than battling monsters. In fact, the player encounters almost none of the monsters from the original Thief except for burrick heads mounted as trophies in some of the mansions, and a few zombies and apparitions.
This is a "mod" for thief 2 called Ultimate Difficulty. PLEASE read the readme. I do not claim credit for this file, I'm simply uploading it for convenience for any moddb members who are looking for thief downloads.
Taken directly from his readme, this is a guy who is from the TTLG Forums and created the Ultimate Difficulty "Mod" for thief 2. Again, please read the readme included with this file for more details.