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 yearCostello that they began to realise she had planned her own resurrection as a contingency plan.

Seeing the effects on Gwen, 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) However, a massive explosion destroyed much of the Hub in 2009; it is not known if any of the cryo-chambers survived the blast. (TW: Children of Earth: Day One)

Despite the fact much of Suzie's actions fell into her own failed grand plan, Harkness nonetheless later stated that he felt responsible for her death (which is technically correct). (TW: Children of Earth: Day Five)

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.
 * In his book Doctor Who: The Writer's Tale, Russell T Davies reveals that he planned at one point to bring Suzie back for an episode of Season 2 of Torchwood.