Seemings.Essentially: You were once normal, when a crazy amoral member of the fair folk kidnapped you. They dragged you back to their world, Arcadia, and enslaved you. Either their magic, or the magic of the world itself warped and twisted your body, making you into a Changeling. Eventually, you escape, only to find a magical construct- A Fetch, in your place.
So your old life is gone to you. Dead. And now you have to live in fear of the fair folk suddenly reappearing to take you
back.
Or, to put it better:
Player characters are Changelings, humans who were stolen from their lives by the True Fae of Arcadia and kept as slaves or servants. Changelings are no longer entirely human, having been tormented in positively Lovecraftian ways until they were broken in either body, mind, soul, or all of the above, and then rebuilt according to the True Fae's whims. The player characters, and many non-player character Changelings, are those who managed to fight, sneak, run, or trick their way back to freedom and the mortal world, but even when they return they bear the scars of their experience. Their very bodies have been changed into inhuman shapes. Their eyes have been opened so that they can see the truth of things, but they are also beset by hallucinations and tricks of perception. Worst of all is the constant, nagging worry: what if I never escaped? What if this is all a trick... or if I was allowed to leave?
Considered by some to be the single bleakest thing White Wolf has ever written. Well, maybe not quite as bleak as Wraith: The Oblivion was, but cranked up there pretty hard and fast. Definitely a stark contrast to its idealistic predecessor, Changeling: The Dreaming. On the other hand, there is a deep emphasis on relationships and connection that isn't there in other New World Of Darkness games- being only slightly better than humans, Changelings must rely on others- their Motley, their Freehold, their Entitlement- to help them take on most threats and maintain their hold on what sanity remains to them.
“She'd become a governess. It was one of the few jobs a known lady could do. And she'd taken to it well. She'd sworn that if she did indeed ever find herself dancing on rooftops with chimney sweeps she'd beat herself to death with her own umbrella.”
― Hogfather