The storm is breaking on the Horizon.
It's been two months since the battle against Nightmare Moon. Luna is recovering, Celestia is busy turning the government back into a diarchy, and the Mane Six have returned to their lives. All seems well, but when Celestia discovers that half of the power of the Elements of Harmony have been transferred to each of the Bearers, she decides to send thirteen mysterious members of the Royal Guard to monitor them as they manifest and develop their new abilities.
The sins of a forgotten war still linger, and an ancient evil lurks in the shadows, just waiting for the right time to strike. The Mane Six suddenly find themselves once again at the heart of a conspiracy to bring about Eternal Night, and only by awakening their powers and realizing their full potential can they do anything to stop it. Friends both old and new will help them along the way, and an unseen force will guide them as it seeks to right a wrong made thousands of years ago. The Bearer's journeys will take them outside the borders of Equestria and into the world beyond, and when they return, they'll have the power and experience necessary to save the world and bring about balance in all things.
The Powers of Harmony TV Tropes Page (SPOILERS)
Thanks to Wildy71090 for the cover pic.