We'll carry on.
Thief: The Dark Project is 25 years old, but it's still one of the best stealth games around, with an active community making fan missions for both it and The Dark Mod, a standalone recreation made with the Doom 3 engine of all things. The Black Parade is for Thief Gold rather than the Dark Mod, the definitive 1999 rerelease with extra maps, which is the version you'll find going for seven bucks on Steam today.
The Black Parade is the work of a team called Feuillade Industries, led by project director Romain Barrilliot. Barrilliot currently works as a level designer at Arkane Lyon and has credits at 3D Realms and Streum On, but he's also a modder, having worked on Sven Co-op for Half-Life and one of my favorite Thief fan missions, The Sound of a Burrick in a Room.
Rather than a standalone map, The Black Parade is an entire campaign of 10 linked missions. When I'm playing fan maps I do miss the original game's sense of narrative, and its delightful protagonist Garrett, which The Black Parade aims to emulate by casting you as a hardened criminal named Hume. Returning to The City after being exiled, you're flat broke and forced to turn to thievery.
The Black Parade comes with half an hour of briefings and cutscenes and 28 voiced characters with 1,800 lines of dialogue. It adds four new tools to your arsenal, more AI movements and a banter system, and a horse. It also gives you the option to move banners rather than cutting them down, make moss patches grow by shooting water arrows at them, pick up the bodies of smaller creatures you've killed, and turn off guards' electric torches. It also gives some of the guards helmets so they can't be blackjacked, lets servants clean up moss and relight torches on harder difficulties, and now zombies can batter down wooden doors rather than politely opening them to get at your tasty brains.