"Day One" was originally seen by 2.3 million viewers, making it one of the highest-rated BBC Three broadcasts of all time, but was met with generally mixed reviews.

Gwen is called into work at Torchwood early when a meteor falls outside of Cardiff, cutting her date with Rhys short.

In an attempt to retaliate, she throws a chisel at him, but misses and cracks open the meteor, allowing a purple gaseous entity to escape.

In an attempt to capture her again, Torchwood run on Toshiko's hunch that she will be after her ex-boyfriend Eddie; they arrive at his house to find Carys already killed him.

After Carys is safely returned home, Jack advises Gwen not to let the job consume her because her perspective is important to the team.

[1] 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.

The scene where Gwen accidentally opens the meteor was meant to "extend the metaphor of breaking the photocopier on your first day at work".

Davies stated "when we're launching a new adult science fiction drama, it's kind of inevitable you're going to do the sex monster."

[2] The episode was originally much lighter in tone, however, the majority of the comedic moments had to be cut on the final script, as they got in the way of the plot.

[1] After it was written, BBC controller of fiction, Jane Tranter, suggested to the producers that the Torchwood team take a "breather" and talk about the mysteries behind Captain Jack while having a Chinese takeway.

[1] Through the read through of the script before filming, Burn Gorman noted that he saw "big smiles" and giggling from several readers because of its content.

[2] To film the exploding rat sequence, episode director Brian Kelly filmed a rat in a cage, and then replaced it with a fur covered condom filled with "chicken bits" and red dye to simulate guts, then exploded it with a squib.

[1] To complete the effect of the gas, 3D artist Paul Burton based his design of the alien from the water creature in The Abyss.

As silly as the idea of a nymphomaniac extra-terrestrial gas is, the cast throw themselves into it with aplomb, quipping their way to the relatively gripping conclusion.

"[10] Patrick Holm of Total Sci-Fi felt that the second episode "equates the word 'adult' with sex and swearing – more of a playground definition than a serious drama.

However, Chris' [Chibnall] painfully simplistic, heavy-handed and often clichéd interpretation of sci-fi (some of Jack's techno-babble is frankly embarrassing) could prove to be a worrying factor later in the series.