Since Russell T. Davies knew the Season 4 finale of “Doctor Who” would be an expensive event, the showrunner understood that he would need to cut corners elsewhere in the season.

While the decision seemed like it would lead to some poorer quality stories, the move actually brought about one of the season’s best episodes: “Midnight.”

Originally, Season 4 was to feature a story called “Century House,” written by Tom MacRae, that would have been Episode 8.

However, Davies shared, “I don’t like the concepts I gave him [MacRae], and I don’t like the overall tone of both 4.7 and 4.8 being comparatively light, fun episodes.”

Another issue were two similar episodes — “Left Turn” and “Forest of the Dead” — that saw Donna trapped in an alternate world, so the show would insert a “double-bank” episode.

This meant that one episode would focus on the Doctor while the other would closely follow his companion, allowing the show to save time and money.

Shot on one set, “Midnight” follows the Doctor on a tour bus in space with sealed windows. The episode features an offscreen monster that could possess the tourists through speech.

Davies shared, “I don’t think we’ve the money for a monster, so it’s sort of psychological terror.” The lack of a monster made creating the ending a challenge for the showrunner.

While pitching the episode to the producers, Davies explained, “It’s all atmosphere. It depends on the tension.” Unlike other episodes, “Midnight” was a completely serious story.

Despite its low budget, “Midnight” became one of the show’s best-received stories, with star David Tennant saying, “It’s quite a grown up script. It’s scary in quite an adult way.”