Denise raised her head. ‘I’ve found nothing in any of Lucy’s old journals, not one reference to his name or appearance.’

‘Then we’ve really got nothing,’ said Harper. He looked up and saw Heming’s face staring out from one of the boards.

‘Where did you disappear to, Heming?’ said Harper. He stared at the pictures of Lucy and Abby. They might be both alive, somewhere out there, with a man intent on torturing and killing them. Harper looked up again at the board. Something was speaking to him, he just couldn’t quite hear it.

Back at the start of it all, they still hadn’t worked out how the killer had enticed David Capske to East Harlem. Maybe there was something in it. They’d made so many small discoveries — the whole Nazi story — but none of it led to the killer. They knew so much, but so little. Then something emerged. He hit the desk.

Denise looked across. ‘What is it?’

‘Your profile, Denise. Listen, I’ve had this feeling all along. This terrible feeling that he’s always ahead of us, always in the know.’

‘What are you saying?’ said Denise.

Harper pulled out his shield and looked at it. ‘Remember the bird of prey that Ruth Glass chose? A blue eagle. We thought it was the Eagle of the Third Reich, didn’t we? We fell into that trap. Listen, Denise, the killer took a big risk in taking those kids. I think they hold the key.’

‘But they won’t let us near them. You’ve no idea where they are.’

‘Maybe they’ve already given us the answer,’ said Harper.

‘What do you mean?’

‘The cop who came out of Lukanov’s apartment. He fooled the detectives, right? And you know what else? I even think that’s how he got away with staying so long at the bodies.’

‘I don’t follow,’ said Denise.

‘How the hell did he drive the Auxiliary truck to the heart of a police operation without impersonating a cop?’

‘I still don’t see what you’re driving at.’

‘I’ve got an idea.’ He looked at Denise. ‘Come with me.’

Lock-Up, Bedford-Stuyvesant

March 14, 4.43 p.m.

Lucy looked all around her. She was in a brick room with a barred window. She looked up at the ceiling. Four shower heads.

She knew enough about history to know that this was no shower. She looked out of the Plexiglass and saw the metal tubes leading to the bin. She had smelled the strange smell from inside the van. Almond.

Outside, in his antechamber, a man was sitting on a chair staring into the window. It was him. Someone she had known. Someone she had made a mistake about. An evil man. He was concentrating. He clenched his fists hard in their leather gloves.

He walked through to the next room. He didn’t appear to want to look at her. He returned with a metal can and walked over to the plastic bucket. Lucy watched him, terror in her eyes. She placed both hands on the Plexiglass and hit hard.

He would not look at her. He took the new can and opened it. Poured the whole tube of Zyklon B pellets into the plastic bucket. Then he turned and stared at Lucy. All he had to do was open the channel.

She tried to recall events, but her mind wasn’t functioning. He must have drugged her. She couldn’t remember things in the right order. Lots of the last few hours were blank. She could remember further back. She was his girlfriend, the love of his life, his black-and-white happy ending, his meaning, his everything. Not someone else’s.

He walked across to the cell and stared inside.

‘You’re going to die,’ he said, and smiled. ‘Once upon a time, you made me sane. Just the warm curl of your skin and the smell of your neck — that’s all it took, and the hatred was a world away. You gave me redemption, Lucy, then you took it away.’

She stared up at him, the tape around her mouth preventing her from speaking, preventing her from pleading.

‘You were more than my lover. You never understood that you were my antidote. You were my hope and you left me.’

He pressed his face against the Plexiglass. ‘I have so much hate and anger inside me now, Lucy, that I can’t get rid of it. I have killed because of you. Then I realized why you hated me. Because you want a Jew for your bed.’ He reached out his hand. ‘I still want you, but I hate myself for it. You excite and repulse me. I found someone who looked like you,’ he said, through the Plexiglass, ‘but she wasn’t enough. She didn’t feel like you, Lucy. She didn’t have what you have. Her name is Abby. She was bigger than you, Lucy. I had to starve her just so I could feel her ribs like I could always feel yours.’

Lucy stared out, shocked and silent. She was going to die. She knew it with horrible certainty.

Central Park

March 14, 5.15 p.m.

Harper drove down the side of Central Park with Eddie and Denise in the car.

‘Where are we going?’ Denise asked.

‘To test a theory.’

‘What theory?’

‘Just keep your mind open and try to think of what kind of person this could be.’

Harper turned off and parked in East Drive surrounded by trees. He got out of the car. ‘Hear that?’

‘No,’ said Eddie.

Denise got out of the car too. ‘Nice to hear some wildlife,’ she said. ‘It’s been an intense few days.’

‘So many birds in this little park. Makes you think.’

‘About what?’ said Eddie.

‘Life,’ said Harper. ‘Makes you think about life.’

‘What the hell is he on about?’ said Eddie. ‘We came to hear a theory.’

Harper took out his NYPD shield and opened it up. ‘I needed to tell you this somewhere private. Away from the rest of the team. Away from all the cops we know and love.’

‘What is it?’

‘Look at my shield. What do you see?’

‘A police number,’ said Eddie.

‘A gold emblem,’ said Denise.

‘And what’s in the emblem?’

‘An eagle,’ said Denise. Her voice dropped. The sound of birdsong rose high above them.

They stopped. Denise and Kasper suddenly saw where Harper was going.

‘When did it click?’ said Denise.

‘A few hours ago. I’ve just been turning every angle in my head, trying to see if I’m thinking straight.’

‘And are you?’

‘Yes. I’m sure of it. Think about it. It clicked for me with the children. I couldn’t make it work out. How the hell did this killer lure Capske into East Harlem? How did he lure Becky Glass off a street into an alley? How the hell did he dare to sit with Capske all that time? He’s a cop.’

‘You can’t be serious,’ said Eddie. ‘How the hell could this happen?’

‘It’s the only thing that pulls this all together. He knew the safe house, right? He knew how many people would be there. Christ, he even knew the weak point between shifts. He knows so much, it’s the only possible answer.’

‘You might be right,’ said Denise.

‘I’ve been thinking about Denise’s psychological fingerprint all day. We’ve got a killer who is fixated on Lucy Steller, a non-Jewish girl. She throws him off. She gets together with a Jew. And this guy’s got levels of anti-Semitic hatred so deep he’s never really acknowledged them, and this is the trigger. She leaves him and he kills someone who looks like her. A Jew. Esther Haeber. Then he abducts a girl who looks very like her. Maybe to try to replace her. But he can’t deal with the lover, David Capske. So he kills him, then tries to disguise it. And now he’s in love with his own power.’

‘Damn right,’ said Denise. ‘Lucy’s the trigger. He starts to stalk her after she ends it, then he starts to hassle Jews, and blame them, then he kills one. He starts to let this fantasy grow.’

‘Then, he joins Section 88,’ said Harper. ‘But never as a member like the rest. Why conceal his identity even then? Because it would show up. Because he knew, even then, back at the start of this. He’s known all along. How to kill in different precincts, how to stage, how to keep Abby from being fully investigated.’