In the midst of World War II, Enigma codebreaker Alan Turing has created a machine named Nautilus that can send a message back into the recent past. After Turing uses it to help the Allied forces succeed on D-Day, he sees the power (and potential danger) of what he has created. He knows he can only entrust it to one person: Joan, the mother of his secret child.

Over the next 70 years, the Nautilus is passed down through the Turing family, who all must decide for themselves when to use this powerful invention. Will it save the world – or destroy it?