As far as you can remember. None of us know how we got here...it's not too hard to believe that you were exposed to a Clockwork and had your memory of it wiped.

It helps make sense of something that's been confusing me, too. Why kidnap someone who doesn't bleed, when blood and the life force it carries are the point of the sacrifices? A virus that turns you into something half-organic would be a perfect solution.