This story is a sequel to World of Ponies: The Pony-Human War

In the nine years since the end of the war between Equestria and the new nation the Empire of Man, the world has seen conflicts and change come and go. But in the highest reaches of the north, the Crystal Empire has stood largely unaffected by these changes. But now all has changed.

A terrible plague has struck the empire, and with it a dark threat begins its return.