A man is transported to Equestria through some unknown means. Instead of becoming the life of the party in an instant, he is forced to survive using less than conventional means, hiding from the denizens of Ponyville in fear of how they would react to a human being. But such an existence cannot last forever.

As well, he must contend with the reality of an incomplete cartoon world. Things are not as easy to adjust to as they seem.

Beyond Earth and beyond the Universe within which Earth exists there is a place full of love; the richest mine of love that can be found, as it is seen by those capable of utilizing it...

Within that place, specifically a part of it called the Everfree Forest, awakes one such creature: a Changeling; specifically, a Changeling who had been a human on Earth the day before. How will he survive in a body that literally needs love for nourishment, while in a world that is now wise to the Changelings' tricks and has branded them evil? Better question: Will he be able to change more than his physical appearance?

These questions are not the only thing that will plague him, for the hows and whys of his arrival and transformation are in a hurry to reveal themselves, and Equestria's heart will stop as it waits for its fate to be decided.

Now with a side story (with more to come) from other characters' POV!
POV: MANE SIX

After the defeat of Discord, the spirit of chaos, the birthrate of Equestria mysteriously comes to a standstill. With no new foals, the pony population quickly declines. Decades later, with the passing of the last pony, Celestia and Luna enact a plan to undo what has been done. Does their salvation lay in an all-too-familiar stone statue in the royal gardens, or is the pony race doomed?

Spike has been rejected by Rarity after helping her for a very important client and a fashion show. He disappears shortly afterwards, leaving Rarity, Twilight Sparkle, and the rest of the gang saddened by his absence.

It has been three years since that incident, and the girls have gotten past the sadness, but still get together to remember the purple dragon every year. On this day, a new pony comes to Ponyville, and although he knows nothing of what his life was like, helps the group have more fun and fills part of the hole left in their hearts from Spike.

Idea for the fashion show goes to LordPlagus777's story Heart of Scales.