Torchwood Four

Torchwood 4 is, or was, a branch of the Torchwood Institute. The nature of this branch, its location, and its personnel are at present unknown. According to information passed from Torchwood 3 leader Jack Harkness to new recruit Gwen Cooper, Torchwood 4 is lost, though there is hope it may be found one day. (TW: Everything Changes)

Behind the scenes
No further information regarding Torchwood Four has, to date, been provided on screen. Some fans have suggested it could have been located in Ireland.