She entered Badock’s Wood at Lakewood Road along the hard tarmac path. The weather and the hour meant that few had yet ventured out. She passed two dog walkers and a few cyclists, crossed the River Trym and took a right along the river path, settling in to her rhythm, enjoying the wood and the freedom it represented. Such a welcome haven in the heart of this city, Anna thought. Others had found this space of significance over the millennia. A Bronze Age barrow in the northwest corner attested to that. They’d brought their dead to this sacred place, but Anna relished it because it allowed her the space to feel alive.

She’d completed two-thirds of the loop, and was on the return leg along a soft woodland path, when her phone rang. Unslinging her backpack, the ring tone told her it was her work mobile. Panting, she accepted the call.

‘Hello?’

Slack answered. ‘Morning, ma’am.’ He paused, hearing her breathing. ‘Is this a bad time?’

‘No. Morning run. Need I ask if you’ve seen the newspapers?’

‘Uh, yes, ma’am.’

‘Any ideas as to who did it?’ She stood on the deserted path, gazing up at the few leaves clinging on to the branches, waiting for Slack to explain.

‘Someone in Thames Valley let it slip, ma’am. Some reporter contacted them claiming they had a source from inside prison who’d tipped them off about a likely link.’

She lifted her face to the sky. ‘Shaw. I might have bloody guessed.’

‘You know who this is?’

She snorted, and when she spoke her words were bitter as acid. ‘I do, Sergeant. And God, do I keep underestimating him.’

‘I do have one bit of good news. Your hunch. You hit the jackpot with the infertility clinic. You were right, they did have frozen semen samples. For legal reasons, they do genetic work-ups and a full DNA profile as a matter of course. They’ve had one or two problems of disputed paternity. You know – a redhead in a family of blonds – that sort of thing.’ Slack sounded jaunty. ‘They didn’t like releasing the information, but the DNA from Osbourne’s semen matches the DNA from the corpse found on the railway line.’ Anna squeezed her eyes shut to relish the electric surge that pulsed through her. His words confirmed what she’d dared to believe. Words that changed everything. They’d been wrong. All wrong right from the start.

She dragged her tumbling thoughts back to the moment as Slack continued. ‘I got the result five minutes ago. Superintendent Harris is with me but—’

‘But what?’

‘But what does it mean?’

‘Isn’t it obvious?’ Anna started walking, her breathing gradually becoming easier, but her head whirling with the consequences of Slack’s news.

‘Not to me. Osbourne kills Emily, Nia and Gail and then decides to top himself. It doesn’t make sense.’

‘It makes perfect sense if you’re Charles Willis.’

‘What?’

She spoke quickly, wanting him to understand. ‘What was left of the corpse we found on the railway line belonged to Osbourne. But we were made to think it was Willis. That’s why Osbourne’s in a hundred pieces, to make the ID nigh on impossible. The killer knew we’d go for the clothes and wallet. He knew we’d think it was Willis.’

‘Then where is Willis?’

She looked up as a cyclist approached, stepped to one side to let him pass. ‘Good question,’ Anna replied.

‘Hang on,’ Slack said as a new thought solidified. ‘I thought Willis was blind?’

Anna almost laughed out loud. ‘That’s what he wanted us all to think. And why shouldn’t we when it’s a hereditary condition that his brother most certainly had? But what evidence did we have except for what Charles Willis chose to show us?’ Anna walked slowly on, pausing now and again along the path, turning, seeing the trees and the meadow beyond, but not seeing them either, wanting Slack to see what she had finally understood.

‘But you saw the computer and that screen for magnifying things at Willis’s house, yes?’

‘Exactly. What better way to be the lie than to live it. The inheritance in the Willises’ disease is X-linked, also known as sex-linked because it’s carried by the X genes. The genes that determine the sex of the individual. It means their mother was a carrier. But Charles Willis was by no means sure of contracting the condition.’

She waited for Slack to comment but the stony silence that followed was not encouraging.

‘God,’ she said. ‘It’d be easier if I could draw you a diagram. Look, X-linked disorders are carried on the X chromosome, of which you have one and I have two, being a female. Female carriers of X-linked conditions have an abnormal gene on one X chromosome, which is counterbalanced by a normal gene on the other X chromosome. The normal gene suppresses the effect of the bad one. You with me so far?’

‘Keep going,’ Slack said.

‘That’s why carriers generally don’t manifest the disease. But male children of female carriers will inherit one of those two X chromosomes from their mothers – they inherit the Y chromosome from their fathers and that’s what makes them boys.’

‘Right, I can see that.’

She stood aside as a jogger hurried past, before continuing. ‘So, obviously, they have a fifty per cent chance of inheriting the faulty gene from their mother, but it’s an equal chance each time.’

‘The Willis brothers had an equal chance?’

‘Yes. One could be affected, the other had just as much chance of not being affected. The other could be entirely normal, is what I’m saying.’

‘You mean Charles Willis was faking it? All of it?’

‘Why not? He’d get sympathy from friends and lovers and help from the state. Anything he did off his own bat would be looked upon as a spectacular triumph. He’d seen his brother from close quarters. He’d know exactly how to behave. He had all the equipment.’

‘But he was registered as blind. We found documentation with his name on it.’

‘That means nothing. Registration involves a form filled in by a busy doctor who, more often than not, does it from a set of notes. Charles Willis could have modified any of his brother’s documentation.’

She didn’t think twice when the cyclist that passed her earlier turned around and stopped. It drew her attention momentarily. She watched him take off a backpack and remove something from it, vaguely registering the fact that it wasn’t a water bottle but something else altogether. A camera maybe? The woods were always full of twitchers.

She turned her back on him, her mind on Slack, and took a step.

Slack said, ‘Christ, that puts a whole new twist on things.’

‘I know…’

A dull thud on the tree just to her left drew her attention. She looked up and then around. Had something fallen from a branch? Her eyes clocked something on the floor. Long, a steel needle, with a plastic cylinder and a bright yellow tufted end. She reached down and picked it up. A dart? She pivoted. The cyclist was still there, twenty yards away, pointing something at her. Something with a long barrel.

She stared, momentarily uncomprehending, a frisson of fear squeezing her heart. She felt a sharp, bright stinging in her upper thigh and fell away from the impact, dropping the phone, her hand brushing at a point on her leg and feeling something hard quivering. Her eyes followed, seeing the dart, watching as her hand struck it, reacting as if it were an insect, pulling it out and letting it fall. It looked identical to the one she’d picked up near the tree. Long, a plastic barrel, a fluffed yellow stabiliser tail. But this one looked different, the barrel shorter from having discharged its load. The sting became a burning pain. Dark blood bloomed through her running pants on the front of her leg. She looked up again.

The bicycle was on its side off the path, the cyclist on foot, moving towards her purposefully, tearing the helmet off his head.

His head. Him. The Woodsman.

Slack’s voice from the phone on the floor, tinny but urgent. ‘Ma’am? Inspector Gwynne?’

She turned and ran, up off the path, towards cover, towards the trees. Up the slope, directionless, hearing him behind her, knowing she was quicker than him, trusting her body. If she made the top of the slope, she’d turn left. Back towards the burial mound and beyond it another entrance, a sports centre, people. No more than two hundred metres.

Easy. She was fit.

The pain in her leg slowed her down, altering her gait, but adrenalin was driving her, pushing blood through her heart and muscles. Bringing oxygen and glucose where it was desperately needed. But bringing, too, the veterinary grade ketamine and thiafentanil cocktail from the site of its injection deep in her quadriceps. It reached her brain just as she reached the top of the slope and Anna’s world changed.

Time froze and her legs stopped pumping, her will and her power leeching away in a cloud of opiate-induced wonder. She was near a large tree. Waves of warmth oozed out of it. She stopped to touch it. It felt… wonderful. Anna’s gaze drifted to the first unspent dart still clutched in her hand, its yellow tufted stabiliser looking suddenly and astonishingly vibrant before she leaned over and threw up. But her stomach was empty, and even the nausea didn’t seem to matter.

Noises behind her.

She turned. He was there. Closing down on her. He pushed her over and she fell on her back. There was no pain. Even her leg didn’t hurt any more. He dragged her ten yards further into the wood, the dart she’d been clutching spilling out as her head bumped over roots and earth. Her mewling cries were muted and vague as he pulled her away from sight of the path. Out of sight of prying eyes.

His hands tore at her weather-proof jacket and the running vest beneath. She tried to fight him but her arms were moving at a different speed, too sluggish to be effective. His open hand caught her a glancing blow on the head, but his second punch landed square on her nose and upper lip, mashing soft tissues against her teeth. She fell back, hands to her face, the salt in her own blood tasting amazing. He forced her down roughly, but she kept her hands over her nose until he kicked her in the belly. No pain, just a whooping expulsion of air as the breath was driven from her lungs. Something gave, a feeling like a soggy balloon rupturing inside her. She pulled her legs up, making herself a smaller target, but the fuzziness from the drugs slurred her words of pleading, turned her actions into slow-motion puppetry.

He hadn’t spoken a word throughout. The only noise was his rapid breathing through the cycle mask. His eyes, locked on hers, were feral.

Seeing. Not blind.

He ripped off her running pants, the leaves cold and wet on her bare buttocks, before straddling her, his weight crushing, hands ripping, his knees forcing her legs apart. It was then that she knew she was going to die with this man on top of her. It would be his hands on her throat, or a knife in her chest, and all she could think of at that moment was of how she didn’t fight enough. Slack would send help and it would arrive in time to find a still-warm corpse. Tears of sorrow and muted fear mingled with the blood in her mouth as she strained feebly to turn her head away from Willis’s choking hands.

He sat back then, one hand squeezing her throat, the other clutching the glinting knife as it penetrated her breasts in sharp, stabbing bursts. He paused only to watch the blood run as she fought to ease the pressure on her windpipe. These were not deep wounds meant to kill. That would come later. He was playing with her. A cat with a mouse. But then her mind was drifting, lack of oxygen from one strong, choking hand colluding with the drug that was never meant for human use, pushing her towards unconsciousness.

A shadow behind him drew her flickering eyes. A human shape moving quickly and stealthily for its size. Sharp crack like a stick breaking, Willis stumbling forward over her, half turning. Another crack and another. Then the weight was off her. The sudden light above coned her vision, but she heard noises and yells and oaths. She turned her head, willing her eyes to follow.

Two people were struggling. The cyclist on top, knife still in his hand, held there by the second figure on the floor, reaching up, arms shaking from the strain of keeping that arm and knife away.

She wanted to close her eyes, to giggle at the ridiculousness of it, stopped herself in time. She brought her fingers up to touch the blood on her breasts. Her skin felt strange, unreachable. She turned over, wanting to hide herself, wanting to crawl away…until her eye caught the brilliant yellow tuft of the unspent dart that had fallen from her hand. It lay a yard away, intact, the plastic chamber primed, the sharp needle dull with mud.

Another yell and a grunt of effort from the combatants feet away from her. A voice shouting, desperate, ‘Run!’

Despite her confusion, Anna knew she could not run. But she would not lie there, either. She crawled to the dart and picked it up. Sucking and blowing air like a steam train, she remained on her knees, the world swimming about her, and began crawling forwards. The cyclist had his back to her, kneeling over the other figure, limbs trembling with effort.

Moving was taking all her willpower and effort. It would be so easy to lie down, collapse on to the floor. So easy…

No! Not now. Not yet.

Another foot, another, the leaves and dirt sliding like slime beneath her, her head hanging. The men were close. The smaller man could see her, his face grimacing with effort, eyes wide with fear and sudden determination. She reached out, and the cyclist, jolted by her touch, turned to look. The cycling mask had slipped, or been torn off, and Anna saw Willis’s face. Saw it and knew that all she’d surmised was true in the second before she summoned what was left of her energy and thrust the dart deep into the muscles of his back.

She fell, his foot kicking her away, unable to do any more, vaguely aware of the cyclist on his feet, arching his back, desperate to remove the dart, stumbling down the slope to the path, heading for his bike and not reaching it as the drugs took hold and he stumbled and fell.

The world darkened. Anna slid towards unconsciousness, but never quite reached its soothing shores. After seconds that felt like hours, she focused on a face leaning over her, large and craggy, the eyes full of concern. She concentrated, her own battered brows frowning, confused. She knew that face and yet couldn’t name it, because it was the last one she’d ever expected to see at that moment. One hand on the collar of the coat he’d thrown over her; the other still clutching a long black steel baton. He saw her look at it and put it down with an apology.

‘Done its job. I was watching your house. You were becoming the obvious target.’ He squeezed her fingers and she was grateful for it.

‘Thank you,’ she said in a small voice.

‘No, thank you,’ said the craggy face. ‘He was a strong bugger. Stronger than me.’

She found a smile of acknowledgement from somewhere, and tried to push it through her cracked and bleeding lips at the man who had promised Emily Risman’s parents that he would find her killer. At last, retired Inspector John Wyngate had done just that.