Patrik had slept like a log all night. Yet he still didn’t feel rested.

‘Sweetheart?’ No answer. He glanced at the clock and swore to himself. Eight thirty. He really needed to get going; they had a lot to do today.

‘Erica?’ He went downstairs but didn’t hear a sound from either his wife or daughter. In the kitchen he found a pot of fresh coffee waiting for him, and a note in Erica’s handwriting was lying on the table.

Sweetheart, I took Maja to the day-care centre. I’ve been thinking about what you told me yesterday, and there’s something I need to check out. I’ll ring as soon as I know more. Could you find out two things for me? 1. Did Christian have a nickname for Alice? 2. What sort of mental illness did Christian’s mother suffer from? Hugs and kisses, Erica. P.S. Don’t be mad at me.

What on earth was she up to now? He should have known that she wouldn’t be able to let well enough alone. He picked up the phone lying on the table and called Erica’s mobile. After a few rings, he was transferred to her voicemail. He told himself to calm down, since he realized there was nothing more he could do at the moment. He needed to get to the station, and he had no idea where she was.

Besides, the questions Erica had included in her note had piqued his interest. Had she come up with some sort of theory? Erica was smart – there was no denying that. And she often saw things that he’d missed. He just wished that she wouldn’t keep going off on her own this way.

He drank a cup of coffee as he stood at the counter. After a moment’s hesitation, he filled a special travel mug that Erica had given him as a Christmas present. Today he was going to need some extra caffeine.

The first thing he did upon arriving at the police station was to go into the kitchen to have a third cup.

‘So what’s on the agenda for today?’ asked Martin when they almost collided in the corridor.

‘We need to go through all the material about the murder of Christian’s girlfriend Maria and her child. I’ll phone Göteborg and see if we can have the files delivered. I’ll probably have them sent by courier, which means I’ll have to hide the expense somehow, so Mellberg won’t notice. Then we need to check with Torbjörn to find out if he’s heard anything from the forensics lab about the rag and the tin of paint in Christian’s basement. The report probably isn’t ready yet, but we might as well put a little pressure on them. Could you start with that?’

‘Sure, I’ll take care of it. Anything else?’

‘Not at the moment,’ said Patrik. ‘I need to check on something with Ragnar Lissander. I’ll tell you about it after I find out a bit more.’

‘Okay. Just let me know if there’s anything else you need me to do,’ said Martin.

Patrik went into his office. It was so odd how tired he felt. Even all the caffeine was having no effect on him today. He took a deep breath in an attempt to rally himself and then phoned Christian’s foster father.

‘I can’t really talk right now,’ said Ragnar, and Patrik understood that Iréne must be nearby.

‘I just have two questions,’ he said, finding himself lowering his voice, even though that wasn’t necessary on his end of the line. He considered asking Ragnar why he hadn’t said anything about the time the family had lived in Fjällbacka. But he decided to let that wait until they could speak more openly. Besides, he had a feeling that the questions Erica wanted answered were more important.

‘Okay,’ said Ragnar. ‘But make it quick.’

Patrik asked him the questions from Erica’s note and was surprised by what he learned. What did all of this mean?

He thanked Ragnar, ended the conversation, and then rang Erica again. But he still got her voicemail. So he left a message for her and then leaned back in his chair. How did this new information fit into the picture? And where was Erica?

‘Erica!’ Thorvald Hamre leaned down and wrapped his arms around her. Even though Erica was almost five-foot six and had put on a lot of extra weight, she felt like a dwarf compared to him.

‘Hi, Thorvald! Thanks for seeing me on such short notice,’ she said, hugging him back.

‘You’re always welcome. You know that.’ There was just a touch of Norwegian intonation in his speech. He’d lived in Sweden for close to thirty years now and over time he’d become more of a Göteborg fan than people who were born there. A gigantic IFK football flag on the wall attested to his loyalties.

‘How can I help you this time? What sort of exciting project are you working on now?’ He tugged on his enormous grey moustache, his eyes shining.

They’d become friends when Erica was looking for someone who could help her with the psychological aspects of the true-crime books she wrote. Thorvald was a therapist with a successful private practice, but he devoted all his free time to studying the dark side of human nature. He had even taken a course with the FBI. Erica didn’t really want to speculate what might have prompted him to take an interest in this particular topic. The important thing was that he was a tremendously skilled psychiatrist who was willing to share his knowledge with her.

‘I need answers to several questions. I hope you’ll be able to help me.’

‘Of course. I’m always at your service.’

Erica gave him a grateful look and then wondered how to begin. She hadn’t really managed to put all the pieces together yet. The pattern kept shifting, like the colours and shapes in a kaleidoscope. But somewhere there had to be a structure, and maybe Thorvald could help her find it. Before she reached Göteborg she’d listened to the message that Patrik had left her, but chose not to ring him back. She didn’t want to answer his questions at the moment. The information he’d left on her voicemail didn’t surprise her; it merely confirmed what she had already suspected.

After pausing to gather her thoughts, Erica started telling the story to Thorvald. In one long account, without stopping, she told him everything she knew. Thorvald listened intently, resting his elbows on his desk and making a tent with his fingertips. Every once in a while Erica felt her stomach clench into knots, as she heard for herself just what a horrible story it was.

When she finished, Thorvald at first didn’t say a word. Erica almost felt out of breath, like she’d been running a race. One of the babies kicked her hard in the diaphragm, as if to remind her that there was something good and loving in the world.

‘What’s your own opinion?’ asked Thorvald at last.

After a moment’s hesitation, Erica presented her theory. It had emerged during the night as she lay in bed, staring at the ceiling while Patrik slept soundly at her side. It had further taken shape as she drove along the E6 towards Göteborg. She had quickly realized that she needed to talk to Thorvald about it. He’d be able to say whether the theory was as absurd as it seemed. He would tell her if she’d allowed her imagination to run wild.

But that’s not what he said. Instead, he looked at her and said: ‘It’s entirely possible. What you’re suggesting is entirely possible.’

His words made the air escape from her lungs in a mixture of alarm and relief. Now she was positive that her idea was right. But the consequences were almost beyond comprehension.

They talked for nearly an hour. Erica asked Thorvald questions and tried to absorb everything he told her. If she was going to take this theory further, she needed to have all the facts in place. Otherwise it could go terribly wrong, and she was still missing a few pieces of the puzzle. She had enough to see the motive, but there were still gaps. Before she could present her theory, she needed to fill them in.

When she got back in the car, she leaned her forehead on the steering wheel. It felt cool against her skin. She wasn’t looking forward to her next visit and the questions she needed to ask – or what she might hear. There was one puzzle piece that she wasn’t sure she wanted to find. But she had no choice.