Harper used the rocks sticking out of the river as stepping-stones to get to the other side. She tried to form an image of the perpetrator but Natasha’s face kept popping into her head. Lauren had known it wasn’t Natasha, long before the evidence proved it. But the trouble was, you couldn’t put much trust in what Lauren said, because of her condition. For example, her insistence that being in the water had changed the babies: pure fantasy. And yet, it was understandable, because of how frightened she must have been, and probably how guilty that she didn’t do enough to protect them, even though it wasn’t her fault. Harper knew all too well how that kind of guilt worked; how it tapped you on the shoulder at night, telling you that you should have tried harder, known better, fought back. That you, rendered powerless in the moment, were also somehow to blame for that lack of power.

The path on the other side of the river was overgrown, but she could see where the stroller had been forced through. Branches were broken, nettles trodden underfoot. A large log lay across the path at one point. Harper stepped over it. Just beyond were the derelict remains of the mill wheel tower.

The mossy shell of the tower was no higher than a large garden shed, the stone from the upper floors long since fallen into the pit on one side that once housed the wooden water-wheel. There was the opening in the wall, where the stroller must have been pushed through, where Natasha went in to hide from the police and instead found the twins. Harper put her head inside. Spent needles and empty plastic bottles littered the floor of the space, which was partially open to the elements. Imprints of the stroller’s wheels showed in the dust between the flagstones.

So much of this felt wrong, but the meaning of the wrongness eluded her. Truth to Harper was like a blade sometimes, she could see it so clearly, the right and the wrong, the real and the false. This case had a murky cloud surrounding it, the shape of it, obscured. ABC, she thought, get back to the basics: assume nothing; believe no one; check everything. An itch of something at the back of her mind, then. What was it she’d forgotten to check?

Harper took out her phone, flicked open her email and searched her inbox for the mp3 file of the 999 call Lauren had made from the maternity unit just after she had the babies. She pressed the play icon and held it to her ear. As she listened, she started to walk back the way she had come.

The operator was a young man, calm and professional.

“Nine-nine-nine, which service do you require?”

“There’s a woman and she’s trying to take my babies. Help me.”

Lauren’s voice was almost unrecognisable. Shrill and panicked.