The migration algorithm. His creatures moving from habitat to habitat to find food. Yes: He would go back there, to the place where he’d left off programming. He would return to the point in his life when he’d last come through this section of the code, to that night when Joanna’s trip was still new and the bad things that happened were still yet to happen—no! He had to skip over that point (because now he knew too well what would indeed happen). No, he had to get to the Ethan Levin before that. To the Ethan who had first written the message. When was that? Before he’d started at Telligentsia. Who was that? An Ethan Levin still confident, still coding input screens for insurance adjusters, still happily sure of his life with Joanna McCarthy, sturdy-legged environmental activist turned administrator, who came home from riding her bike to do wonderful things to him in the shower.