Torchwood is set in Cardiff, some time after the Doctor Who series 2 finale Doomsday, making it likely sometime in 2007. It follows the Wales branch of a covert agency called Torchwood, that investigates extraterrestrial incidents on Earth and scavenges alien technology for its own use. To paraphrase Torchwood Three's commander-in-chief, Captain Jack Harkness, the organisation is beyond the government, the police, and the United Nations. Their public perception is as merely a 'special ops' group.

The Torchwood Institute was established in 1879 by Queen Victoria, following her harrowing experiences with a Scottish werewolf ( Doctor Who : Tooth and Claw , 2006). As later introduced ( Army of Ghosts, 2006), the modern-day Torchwood Institute was located in Canary Wharf, London. In the first episode of Torchwood ( Everything Changes ), Captain Jack explains that the Cardiff branch is known as Torchwood Three - whereas the Torchwood Institute in London, destroyed during the Dalek / Cybermen invasion, was Torchwood One, that Torchwood Two is a small office in Glasgow staffed by a "very strange man", and that the fourth is simply missing.

Torchwood Three operate essentially as a 5 person team, led by Captain Jack Harkness, played by John Barrowman. The team also has its own medic called Owen Harper, who is played by Burn Gorman and its own technology specialist called Doctor Toshiko Sato played by Naoko Mori. The newcomer to the team is ex police constable Gwen Cooper played by Eve Myles. Finally, there is Ianto, who is essentially an odd job man and caretaker of the Torchwood base in Cardiff. Ianto is played by Gareth David-Lloyd

In an October 17, 2005 announcement, BBC Three controller Stuart Murphy described Torchwood as "sinister and psychological... as well as being very British and modern and real." it was further described as "a British sci-fi paranoid thriller, a cop show with a sense of humour... dark, wild and sexy, it's The X-Files meets This Life ." As Torchwood is a post watershed show - that is, after 9.00 p.m. - it has more mature content than Doctor Who.

The show can therefore be a bit more visceral, more violent, and more sexual, if it needs to be.