Suzie Costello

Suzie Costello was a member of Torchwood 3 in the early 21st century up until late 2007 when she commited suicide.

Although she wasn't alone in having used Torchwood-acquired technology to her own advantage, she had been the most destructive.

Profile
Little is known about Costello personal life or upbringing, save that she loathed her father and had an affair with Owen Harper. (TW: They Keep Killing Suzie)

Suzie Costello found employment at Torchwood 3. She developed a nihilist worldview and found murder as acceptable a means as any for achieving her goals, particularly to unlock the secrets of the Resurrection gauntlet. The gauntlet worked particularly well on the victims of violent deaths. Costello committed a series of murders with the life knife to improve her use of this. Her plans went wrong when she was discovered by P.C. Gwen Cooper. Her attempt to kill Jack Harkness was thwarted when Jack's immortality was revealed. Suzie took her own life and her body was placed in the Torchwood cryo-chambers, and her worldly possessions collected and placed into storage as is common practice for deceased Torchwood Operatives. (TW: Everything Changes)

Later that year, Torchwood 3 investigated another series of murders committed by a "sleeper agent" that Costello had put in place prior to her death, and the team realized that Costello's suicide was part of a greater plan. Torchwood 3 believed Costello held the key to a mysterious organisation known as Pilgrim. Costello had planned this all along, as a contingency plan in case she ever got discovered. A second series of murders acted as inducement for Torchwood 3 to revive her, ironically with the very resurrection gauntlet that Costello had killed for earlier. Cooper wielded the glove this time, but rather than reviving Costello for only a few minutes as usual, the glove instead revived her apparently permanently. This left Torchwood with a quandry since they now had a dead person who had come back to life, yet among other things still had a severe head injury caused by the suicide bullet. Unknown to the team, Costello foresaw this and through a mental link in the glove forced Cooper to transfer part of her essence, which Costello used to heal her mortal injury, an action which slowly began to kill Cooper. It was only after they'd revived Costello that they began to realise she had planned her own resurrection as a contingency plan.

Seeing the effects on Cooper, Jack asked Costello to give up her restored life which, drunk with power, she refused to do. Faced with Cooper's imminent death, Jack had to choice but to shoot Costello down in cold blood, however the link via the gauntlet prevented Costello from dying. Only after Jack ordered Toshiko Sato to destroy the gauntlet did Costello die again, this time forever. Her body was subsequently returned to the cryo-chamber. (TW: They Keep Killing Suzie)

Behind the Scenes
In order to catch viewers unaware with the twist ending of Everything Changes, the first episode of Torchwood credited actress Indira Varma as a regular cast member. She was featured in pre-broadcast publicity for the series.