Katie Russell was Owen Harper's fiancée before he joined Torchwood Three. She was working as a junior doctor at the same hospital as Owen.

Katie was diagnosed with Alzheimer's disease — the youngest case of the disease ever recorded. Owen refused to accept the diagnosis, and ordered examination after examination, but none showed up anything unusual. After a final brain scan, the doctors thought she had a brain tumour. During the operation for the "tumour", an alien creature inside her brain which had infected her acted in self-defence, killing both the doctors and Katie herself, devastating Owen. (TV: Fragments)

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