Gordon decided that the most affecting and "X-Files"-like story should involve a time-traveler who "turns out to be you". Howard was inspired to make the main antagonist a regretful scientist after hearing the story of Manhattan Project physicist J. Robert Oppenheimer berating U.S. President Harry S. Truman for using atomic bombs on Hiroshima and Nagasaki in 1945. This prompted Gordon to rhetorically ask: "What if Oppenheimer could go back to the past and 'uninvent' the bomb?". Soon, Gordon and Greenwalt began pondering fatalistic determinism brought about by the ability to see the future, with the former noting: "Life itself is about the unknown and discovering what is in front of us. But if everyone, or maybe some people, knew what would happen, that would create a new set of horrors, and it would need to be stopped".