She had just reached the gates of Christchurch College when Tansy caught her up. She pushed a wilted business card into Anna’s hand. ‘It’s from the cafe where I work,’ she said breathlessly. ‘I’ve written my number on the back. I just thought, in case you ever—’ She registered Anna’s stony expression and pulled a face. ‘You probably never want to set eyes on us again, right?’

Anna shoved the card into the front pocket of her leather messenger bag, gave a curt nod and kept walking. The autumnal light touched the ancient buildings with gold. Somewhere bells rang, the clangorous medieval sound mingling with the hum of traffic.

Throughout the interview she had longed for the moment when she could go back to her safe solitary existence, not having to monitor her expressions or explain herself. But Inspector Chaudhari had shattered her illusion. I was with the first-response team. It’s not something you easily forget. With those brutally casual words he had shown her that she would never now know any peace of mind.

As she passed Carfax Tower a trio of teenage girls hurried past, laughing, talking, flicking back their glossy hair. She watched them rushing headlong into their unknown future, girls every bit as self absorbed and silly as she had been.

Anna began to walk faster, and her White Shepherd obediently matched her pace. She mustn’t think. It felt like if she could just keep moving she could put actual distance between herself and the rising tide of horror. Without slowing her pace, Anna fumbled one-handed for her ear-buds, plugging herself into a talk radio podcast. She needed impersonal voices; voices, and the physical rhythm of walking.

There had been a dark period in her life when mindless walking was the only thing that had held her together, and so she had walked and walked. Sometimes she’d walked all night. When exhaustion finally stopped her in her tracks, she’d slept – in doorways, on park benches, at the bus station in Gloucester Green – while her grandparents had gone frantic with worry. Once she’d gone missing for two weeks. The police had eventually picked her up on a street just off the Cowley Road. Her grandparents had begged her to tell them where she’d been, but she only knew that she’d been walking. Her grandmother had cried over Anna’s grubby emaciated state. She ran her a bath, put plasters on her blisters, tried to persuade her to eat. For her grandparents’ sake, Anna had made a superhuman effort to behave like a normal sixteen year old: breathe out and in, chew and swallow, even go to school, until the next time the furies in her head drove her to walk out of the door and keep on walking. Twice she’d been caught trying to let herself into her old family home with her grandmother’s key with no memory of how she’d got there.

That lost, driven teenager suddenly felt dangerously close. Anna could feel her grief and terror. She remembered how something from the external world would occasionally break through the muffled undersea sensations that had enclosed her – the smell of mown grass from a college garden, a cafe door opening to let out a babble of voices – before she was sucked back under. She had walked so as not to feel, not to remember. But sometimes, like today, memories would rise up, more disturbingly vivid than when they were really happening. In her memories, everything was burnished, glowing, hyper-real. Whole scenes played themselves out before her eyes. All the times she’d screamed at her mother for being so stupid, for being so unfair, while her little sister looked on, stricken. Worse than Anna’s shameful memories were the ordinary good times; like the time she and her brothers had attempted to toast marshmallows on a beach in Cornwall in a near gale while her dad tried to catch fish for their supper. The marshmallows had refused to melt, then turned ominously black and finally burst into flame. The fish had stubbornly evaded their father’s hook and line. Her dad had ended up buying everyone fish and chips, which they ate in the fish-smelling car with the heater turned up high. Yet Anna recalled it as a day of pure unalloyed happiness.

If she could just bring them all back for one hour, just one hour . . .

Anna found herself sitting on a stone step. She could feel the chill of the stone rising up through the denim of her jeans. She was soaked through with cold perspiration. Tiny black specks danced before her eyes, and for a moment she didn’t know which Anna she was supposed to be. Then she became aware of the solid warmth of her White Shepherd pressing firmly against her hip, pulling her back into present time, back into her body. Anna dimly heard a passer-by say, ‘That’s the most fabulous looking dog I have ever seen.’

And she remembered Naomi smiling up at her, her arms wrapped around Bonnie’s neck.

Anna had offered to pay her for her investigations, and Naomi had laughed. ‘Are you kidding! Finding out stuff is like my drug of choice! I’m so lucky,’ she’d told Anna as rain battered the car windows. ‘I actually get to do what I love every day!’

Bonnie continued to press insistently against Anna. It felt as if she was saying, ‘Are you OK? If not, I will make you OK.’

Properly taking in her surroundings for the first time, Anna saw that she was sitting on the bottom of the flight of steps at the base of the Martyrs’ Memorial, just across from the Randolph Hotel. All she had to do was cross over to the Banbury Road, keep walking, keep breathing out and in, and eventually she’d reach her front door. She pulled herself shakily to her feet.