 Captain John Hart appears through the Cardiff space @-@ time Rift using a vortex manipulator and asks Jack Harkness for help in locating three radioactive cluster bombs , apparently scattered across Cardiff . Jack Harkness tells his team that John cannot be trusted but agrees to help him . True to Jack 's word , Captain John is lying and seizes the containers , trying to kill Gwen Cooper ( Eve Myles ) using a paralyzing lip gloss , shooting Owen Harper ( Burn Gorman ) and pushing Jack off the top of a building , thinking he 's dead . However the containers , which are supposed to contain the location of an valuable diamond hidden by the lover he murdered , instead contain an explosive which latches on the DNA signature of her killer . As insurance against Torchwood leaving him to die , John handcuffs himself to Gwen and swallows the key . After superficially altering his DNA using that of the Torchwood staff , Jack and Owen are able to save John 's life before banishing him . Spurned by his former lover , John leaves by means of his Vortex Manipulator . 
