Torchwood Four
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Torchwood 4 was a branch of the Torchwood Institute. The nature of this branch and its personnel was unknown. Jack Harkness stated it was "missing," and declared "we'll find it some day." (TV: Everything Changes). Agnes Havisham claimed that Torchwood Four's disappearance was a "messy business". (PROSE: Risk Assessment)
Its possible that it may be or have been located in Northern Ireland as Queen Victoria mentions "We must protect our boarders on all sides". (TV: Tooth and Claw))