Torchwood Four

Torchwood 4 was a branch of the Torchwood Institute. The nature of this branch, its location, and its personnel where unknown. According to information passed from Torchwood 3 leader Jack Harkness to new recruit Gwen Cooper, Torchwood 4 he told her it was lost, though there was hope it would 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. This would seem to indicate that Torchwood 4 was 'lost' when Ireland gained independence from Britain in the 1920s, after the Torchwood Institute was formed.