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Nancy was the single mother of the "Empty Child", Jamie. She lived in London during the London Blitz and she helped the Doctor restore normality to war-time London.
When Nancy was around sixteen years old, she became pregnant. Due to the stigma surrounding unwed teenage mothers in the 1930s, she told her son, Jamie, that she was his sister. In January 1941, Jamie was killed in an air raid near Limehouse Green station, but Chula nanogenes partially revived him as the Empty Child. The virus spread to other humans at Albion Hospital.
Because of her son's death, Nancy took it upon herself to look after children who had been evacuated during the London Blitz, but had returned as strays. She stole food from families as they hid in air-raid shelters. Nancy met the Ninth Doctor during one of these meals and warned him about Jamie. She suggested he ask Dr Constantine at Albion Hospital for information.
When Nancy told the Child, who kept asking for his mummy that she was his mummy, the nanogenes reprogrammed themselves, restoring Jamie and the other infected humans to normal.