Mirror Edinburgh
A version of Edinburgh was in a pocket of unreality that was connected to N-space via two of Silversmith's mirrors. It was the exact opposite of the real Edinburgh in that what was a theatre in the real world would be a prison in the mirrored world.
When people entered the mirror, a different mirrored version of themselves would come out called Mirror Folk.
Silversmith unwittingly created the connection between this dimension and the real one and, when he stepped in, he was imprisoned by the Mirror Silversmith. The Mirror Silversmith harvested his psychic energy to power the city and put on shows to capture more people to harvest them of theirs. He planned to replace real people with the Mirror Folk.
The Eighth Doctor and Josie Day rescued the captured humans and the real Silversmith and broke the connection to the Mirror Edinburgh. (COMIC: The Silvering)