What if we were slowly being invaded, but no one realized it.
What if no one realized it because the invaders were able to devour a person and then take on every aspect of their appearance and the ability to perfectly mimic their personality for other humans.
What if this has been going on for years, and they've been slowly integrating themselves into society, becoming the world leaders, the rich, the big names.
What if they're taking over the average people too? Your friends, your spouse, your family, your neighbors, the waitress who took your order yesterday?
What if you're the last human left?