Luna has fallen into a deep sleep and cannot be awoken. Meanwhile, the night sky dims more and more with every passing moment. The Mane 6 are sent underneath Canterlot for a potential solution while Celestia works on her end.
My very first (self-published) book can be found on Amazon Kindle for 5 or 12 paperback! If you love dragons, give it a look! https://www.amazon.com/dp/B0CSM7QQ2M