 The working title for the episode was "New Girl", which changed to the current "Day One" by the beginning of October 2006.Head writer Chris Chibnall, who wrote the episode, found that writing the second episode was hard, as there was a challenge to demonstrate how Torchwood works, and set the formula for the rest of the series.He wanted to write an episode that would centre on Gwen about her "first day in hell", and show the audience that Torchwood is unlike any normal job, as one small mistake can have major ramifications on the city.