Torchwood S01 E04 Cyberwoman

"Save the Planet (One Alien at a Time)"

A Ianto themed episode Ianto Jones hides a very big secret at Torchwood - his half-converted girlfriend from the Canary Wharf Battle - down in the basement. He is quick to hire a Japanese doctor who believes he can "cure" her. But things soon go wrong, and the Cyberwoman's destructive powers are released to the whole of Torchwood. Upgrading is compulsary.