S01E04: 'Cyberwoman'

Ianto Jones has been hiding a secret deep in the vaults of Torchwood - his partially cybernised girlfriend Lisa.

Rescued from the offices of Torchwood's London HQ in the midst of a Cybermen invasion (as seen on Doctor Who), Lisa has been kept alive by Ianto in the hope that she can be healed. But his covert attempts to involve a cybernetics expert in restoring Lisa to her former human glory end in bloodshed when she attempts to convert him into a cyberman.

Lisa goes on the rampage and drains the Hub of its power - thus alerting the Torchwood crew to her presence. As they track her down, an emotional Ianto remains protective of her and works against his colleagues.

Jack is soon seemingly killed by Lisa, Owen and Gwen become slightly frisky when hiding together, and Torchwood's pet pterodactyl discovers that cyberwoman coated in barbecue sauce is rather appetising...