While she waited for the telephone number to be checked, Carla started to dig into Joanne’s and Eve’s backgrounds. She opened Google – police databases were good, but they couldn’t compare with the World Wide Web – and it didn’t disappoint: ten minutes in and she’d got more via the press than ten hours of searching on Thames Valley’s system could ever have achieved.

As Carla scanned the articles she grew increasingly intrigued; it was as if Joanne Fowler’s and Eve’s histories were mirror images of each other, but with hairline cracks that diverted each intended course. But what if those cracks had converged, as Nell believed? Was it possible their paths had crossed before Joanne’s child had died?

Carla wrote down what she knew. Articles written during Joanne’s trial told her the woman had been taken into care at birth. She’d spent two years in a foster home – three miles from Eve’s childhood home – before being adopted by a schoolteacher and a university professor, both upstanding members of the community. The articles asked repeatedly, ‘How could a woman from such a family become the evil murderer we see now?’ All relied on lazy stereotypes about the genetics of evil – ‘some people are just born that way’. Carla didn’t believe that. For her, actions stemmed from life experiences, not a dodgy gene pool, and if the last eight years as an analyst had told her anything it was that criminals came in all shapes and sizes, from all sides of the class divide.

The papers told her Joanne had met her husband at university in Solihull and they’d married soon after graduation, living for three short months in a rented property on Cowley Road, Oxford. They hadn’t come to the attention of the police until the death of their child, which was seemingly when Eve entered their lives.

Information on Eve was harder to come by. HR held some, but it was limited and incomplete. What Carla did find was that Eve had been admitted to a Portsmouth care home aged fourteen after her stepfather’s abuse had landed her in Portsmouth General and concerns for her welfare had become too loud to be ignored. After two years Eve left the home, moved to Reading and a few years later began work as a civilian in the police – forensics, but low level, due to her lack of qualifications. After marrying Gerry, at some point Eve must have gone back to school, because ten years later she had a university degree and a job with the Home Office. But the gap of ten years was unaccounted for. Eve had not been employed by Thames Valley Police or the Home Office, and there was no account of when she had moved to Oxford, or why.