‘What do you mean, he can’t come here?’ Patrick had said to Suzanne after she’d got off the phone to the Met’s press bureau, who had asked to be kept informed of all developments in the case.

She gave Patrick a calming smile. ‘I’ve been told that if Shawn Barrett comes to the station, it will be on the front of every tabloid in the country tomorrow, every celebrity gossip site; there’ll be fans blocking the doorways; photographers sticking their cameras in our faces . . . It will be mayhem. Until we get to the point where we’re actually going to charge him, when we’ve got a rock-solid case against him, we need to go to him. Discreetly. He’s agreed to meet you at his apartment in Chelsea Harbour.’

‘Agreed . . . ?’

‘Patrick, don’t be grumpy. It really doesn’t suit you.’

She came across the office, glancing through the window to check no-one was watching, and laid a hand on Patrick’s arm. He felt the current run from the point where she touched him through his veins into his chest.

‘We don’t have any evidence to prove it’s him,’ she said.

‘Yet.’

‘And until then, I’m afraid we have to play by their rules. Do you really want to be on the front page of The Sun tomorrow?’

So here he was, standing behind the van driver and looking down at the grey, churning Thames through the wall-to-ceiling window outside Barrett’s apartment, on the twelfth floor of a building that was home to a collection of Russian oligarchs, movie stars and bankers. Patrick had looked it up on the way over: a two-bedroom flat at this address cost upwards of £4 million. And this wasn’t Barrett’s only home. He also had places in Los Angeles, Ibiza and Stoke-on-Trent, where he had bought not just the ex-council house that he grew up in, where his mum still lived, but the entire street. According to the news story, Mrs Barrett didn’t want to leave her beloved two-up two-down, so Shawn had bought all the houses around it and was paying for the street to be turned into a kind of country estate, with landscaped lawns, pools full of koi, a sauna house (‘My mum loves her saunas’) and a garage full of Bentleys, slap-bang in the middle of the city. You couldn’t make it up.

The door opened and a man Patrick recognised took the tower of boxes from the van driver. Reggie Rickard, OnTarget’s manager. Rickard spotted Patrick, nodded at the driver and put his finger to his lips. Only when the other man was safely in the descending lift did he say, ‘Lennon.’

‘Detective Inspector Lennon.’

‘Ooh, sorry.’ He smirked. ‘Did any of the paps try to talk to you, ask you why you’re here?’

‘Yes, and I told them that Shawn Barrett is a sex offender who I’m questioning in—’

‘For God’s sake, man. Come inside.’ Rickard ushered Patrick in, flapping his arms and peering up and down the corridor. His eyes nearly popped out of his head, making Patrick think of a squeezed hamster. ‘You didn’t really . . . ?’

‘Of course I didn’t.’

Rickard pointed at him. ‘Ah-hah! A cop with a sense of humour. I like that. Mervyn didn’t mention that.’

I bet he didn’t, Patrick thought.

‘Anyway, come in. Shawn’s looking forward to meeting you, showing you what a lot of nonsense this all is.’

Patrick followed the other man down a short hallway, which opened up into a cavernous living room, flooded with light from the windows that gave a spectacular view across Battersea Park. A huge canvas hung on the opposite wall – a cartoonish scene created by a famous Japanese artist whose name Patrick couldn’t remember. The equally vast TV was on, the sound turned down, a PlayStation 4 plugged into it, with games piled up on the floor, spilling from their cases. And at the far end of the room, perched on a black leather sofa with his legs curled beneath him, sat Shawn Barrett, his floppy hair falling over his eyes, a bored expression on his face. He was staring at his iPhone.

‘Shawn, this is Detective Inspector Lennon.’

The boy-band singer looked up. His eyes seemed glazed, not showing much sign of activity behind them. Was he drunk or stoned? Then Patrick remembered Barrett always looked like this, except on stage or in his videos, when he would adopt a cheeky grin and turn on the charm.

‘I come alive when I’m performing,’ he’d said in an interview Patrick had read online last night; an interview in which every line Barrett uttered came straight out of the Big Book of Pop Star Clichés. This guy was so media trained, Patrick suspected, that the chances of a journalist ever getting him to say anything interesting were somewhere between zero and none.

‘Lennon,’ Barrett muttered. ‘Like that guy . . .’

‘John Lennon,’ Rickard said gently. ‘From The Beatles.’

‘Oh yeah! Love them.’ He squinted at Patrick. ‘Are you related?’

‘I don’t think so.’

‘Oh.’ Barrett turned his attention to his manager. ‘Did my deliveries come?’

‘Yeah, Shawn. Hang on a tick.’ Rickard left the room and returned with the pile of boxes, which he set down on the floor in front of the sofa. Barrett began immediately tearing them open like a five-year-old on Christmas morning, scrutinising each video game, DVD or gadget before tossing it aside. Only once did he pause, exclaim ‘Awesome!’ over some PS4 game, before moving on to the next parcel. Soon, the floor was covered with brown cardboard.

‘Do a lot of online shopping?’ Patrick asked, halfway through this display.

Rickard answered. ‘These are from Shawn’s Amazon wish list. He lists whatever he wants and his fans compete to buy the stuff first.’ He laughed. ‘I’ve had to ask Shawn to restrict the amount of stuff he adds to the list. The delivery company can’t cope.’

Patrick noticed that the pop star didn’t bother to read the notes that came with each gift.

After Shawn had tossed aside the last item, he returned to staring at his phone. ‘Tweeting,’ he said. He thumbed the screen, concentrating hard. ‘There you go.’

‘What did it say?’ Rickard said, checking his own phone. Patrick realised the manager was worried Barrett might have tweeted something about his own presence. A look of relief crossed the manager’s face. ‘“Just chillin.” Nice one.’ He winked at Patrick. ‘Bet that gets ten thousand retweets.’

Patrick tried hard not to roll his eyes. He scrutinised the young man before him. Could he really be a savage murderer? It seemed difficult imagining this spaced-out kid gathering the energy to make a sandwich, and it was equally hard to picture him persuading a girl to join him in a sadomasochistic sex session – let alone be powerful and cunning enough to do what the killer of Jess and Rose had done. But he knew for a fact that Barrett engaged in S&M. And Barrett had enough drive to achieve what millions of teenage boys only dreamt of. It couldn’t purely be luck; surely Barrett wasn’t a mere puppet? This slacker puppy act had to be just that: an act.

Patrick sat down in a leather armchair opposite Barrett, with Rickard hovering close by. ‘Shawn, thank you for agreeing to talk to me. I need to—’

Barrett interrupted. ‘What kind of music are you into?’

Patrick decided it wouldn’t do any harm to act friendly. ‘My favourite band are The Cure. Have you heard of them?’

To Patrick’s surprise, Barrett’s eyes lit up. ‘The Cure? Oh yeah, my granddad likes them.’

‘Your granddad?’

Rickard interjected. ‘His grandfather’s about your age. Shawn’s mum had him when she was seventeen. And her parents were teenagers when they had her.’

‘Yeah,’ Shawn drawled. ‘He’s into all that eighties stuff. Depeche Mode, The Human League. That miserable bloke – what’s his name? Morrissey, that’s it.’ To Patrick’s even greater surprise, Barrett started singing one of The Smiths’ songs, ‘Panic’. So he really could sing: his voice was bland but tuneful, and Patrick could imagine how horrified Morrissey would be if he heard this rendition of his song.