King Sombra was not killed after "The Crystal Empire". You cannot kill that which isn't alive, after all. Instead he was reduced to a mere shadow of what he once was, barely clinging to life. But now, months after the Crystal Heart nearly destroyed him, Sombra is back for vengeance upon the ponies who thwarted him. Focusing his wrath on Twilight Sparkle, the Shadows King leaves Twilight with precious little time to solve the mystery of the mysterious force terrorizing Ponyville... And making her friends disappear, one by one...