Who am I?

From PlotBunnies

A youngish man wakes up in the middle of the desert, he knows nothing about who he is, where he is or why he's there. He just has a nagging feeling in the back of his mind that he has until sunset, there's a woman who's counting on him. He can't shake off the feeling that it's absolutely essential that he does whatever he's supposed to otherwise she will die. But, what on Earth is he supposed to do!? Who is she? How did he get into this situation? And, how does he get out of it...?