The North, an unknown place. Princess Celestia plans to change that. Under her authority, an expedition shall be established to head north and record what they have found there.

The leader of the expedition, of course, is Twilight Sparkle, along with her friends. Tagging along will be Shining Armor and a few of his soldiers, and Princess Luna as an ambassador in case they find any locals.

What they find, however, is more than the expected.

The Snow Ponies. A group of primitive ponies categorized by Twilight to be a type of earth pony.
The powerful Thunderbird, a majestic eagle that soars the northern skies and keeps watch over everything, it is considered as a god by the snow ponies.
The dancing sky lights, also known as the Aurora. Legends say that the lights a inhabited by ponies who have passed on. They now dance within the lights and watch over those they have left behind.