Torchwood is touted as a sci-fi crime thriller for adult audiences, which will follow the adventures of a team of renegade investigators, led by the enigmatic Captain Jack. It will see the investigators scavenge alien technology in a very real world to solve crime, both alien and human.

Russell T. Davies said that it was always his intent to write Barrowman's character off Doctor Who. "We only ever booked him for five episodes. I mean, a bisexual con man from the 51st century: Did you ever think that was going to work? On paper, I had doubts about it myself. So I thought, 'Oh, five episodes of that will do!' I thought he would run out of charm by then. But he turned out to be the most extraordinary success, which was John, I have to say, and all of the writers loved writing for him."

Davies told SCI FI Wire it is definitely darker than its predecessor. "I would call it modern urban sci-fi, really. It's a little bit harder science fiction than Doctor Who is, although, again, it's very character-driven ... it's very different territory to Doctor Who. It's not about fleets of spaceships and invading monsters. It's more about ideas, like 'What if you could read someone's mind?' It's quite X-Filesy in that way. The X-Files has been off our screens for far too long, and it's a marvelous show. So we've got elements of that in it, because it works."