Tirek reigns supreme. Three of the four princesses are trapped in Tartarus while the fourth one is hiding, not even able to control her immense powers. Tirek has brought Discord, the second most powerful magical instance of the world, to work for him, claiming that they would rule together. He thinks that he has already won. That he knows the outcome of the game, and that no one could possibly stop him anymore. In his arrogance, he doesn't even think of the possibility that he could be the one who is being manipulated.

Deep down under the Castle of Friendship, a building that stands for peace and harmony, lies one single cell, containing one single inhabitant, buried under the castle and under the personal supervision of Twilight Sparkle herself. It is up to the Princess to deal with one of the sickest and most brutal ponies in all of Equestria - who seems to have developed a strange interest in his keeper.

In this alternate timeline, King Sombra was able to return to the Crystal Empire. It is now at Celestia to face the consequences and carry the burden that comes with it (it's kinda hard to write a long description to a short story).