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 that since Torchwood One was in England, Torchwood Two was in Scotland, and Torchwood Three was in Wales, Torchwood Four might have been in Ireland.