King Sombra had long been corrupted by darkness. To rid him of it, Radiant Hope was forced to make a terrible sacrifice.

Now, Sombra may be free, but he has lost the only pony he ever really cared about. To get her back, Sombra must descend into the Prison of Shadows and brave the wrath of his own people, the Umbrum. But even with the unexpected aid of Princess Cadance, the quest to save Hope will be a treacherous and perilous one. And as he plumbs the depths for answers, Sombra may find it hard to live with what ultimately comes to light.