 Torchwood was the subject of a background arc during the 2006 series  of _"Doctor Who" (2005)_ (qv), with most episodes containing at  least one reference to the Torchwood Institute, beginning with the  2005 series episode "Bad Wolf" and culminating in the Institutes  appearance in "Army of Ghosts" and "Doomsday". The 2006 episode  "Tooth and Claw" details the origins of Torchwood. After  "Torchwood"s debut, it was referenced again in the Doctor Who  Christmas special, "The Runaway Bride".