Plot summary
Ianto and his girlfriend Lisa both worked for Torchwood in London when Cybermen partially converted Lisa during their battle at Canary Wharf. Ianto has since cared for Lisa by placing her in the basement of the Torchwood Hub in Cardiff with a conversion unit to keep her alive. Secretly inviting cybernetics expert Dr Tanizaki to the basement, Ianto wants Tanizaki to reverse the process. Tanizaki is able to make Lisa breathe on her own again, but by that time, Torchwood is called back to deal with a rogue UFO. When Tanizaki brings Lisa back down to the basement, her Cyberman influence takes over and she kills him by attempting to upgrade him, causing the power to flicker.
Ianto discovers Tanizaki's body and attempts to hide it. Meanwhile, Lisa drains even more power by re-entering the conversion unit. Believing the Hub is under attack, Jack sends Gwen and Owen to the basement where they find the abandoned conversion unit. Jack runs down to find Owen is lying unconscious and Gwen is about to be converted. He stops the process and attempts to shoot Lisa, but Ianto stops him, allowing Lisa to escape. Jack tells Ianto that there is no cure.
Ianto approaches Lisa to reason with her, only to end up being knocked unconscious. Jack buys Toshiko time to go to the surface to recharge the emergency power cells by allowing himself to be electrocuted twice by Lisa, though he survives due to his immortality. To allow the rest of the team to escape, Jack sprays Lisa with a special "barbecue sauce" that summons the pet pterodactyl; as it attacks her, the team escape by the invisible lift. Ianto punches Jack for his actions, uttering he is "the biggest monster of them all." Meanwhile, a pizza delivery girl unwittingly enters the Hub and Lisa implants her brain into the delivery girl.
Ianto runs back to the Hub, but is stopped by Jack, who threatens him at gunpoint with an ultimatum; either he will execute Lisa, or if he does not do so in ten minutes, Jack will enter and kill them both. Ianto returns to the basement where he is reluctant to shoot Lisa. Lisa promises to Ianto that they can be upgraded together. The rest of Torchwood, arriving to hear that, open fire and kill her, leaving Ianto to mourn.
Credits
Adapted from Wikipedia contributors, Cyberwoman. Narrative and paragraph formatting adjusted; illustrations, reference markers and non-story material omitted.