In the midst of World War II, Enigma codebreaker Alan Turing creates a machine named Nautilus that can send a message back into the recent past. When it successfully averts disaster for the Allied forces on D-Day its power and potential danger become terrifyingly clear, and Turing realizes he can entrust his creation to one person only: Joan, the mother of his secret child.

Over the next seventy-five years, the Nautilus machine is passed down through Turing's descendants, who must each decide for themselves if and when to use this powerful invention. But while it has the power to prevent catastrophe, the wrong decision could have devastating consequences.

When the stakes are at their highest, will using Nautilus save the world – or destroy it?