‘Witnesses: get back to Sangora Road, conduct another door-to-door. Karen and her accomplice parked near the pub at around five thirty p.m. There would have been drinkers in at that time, some possibly sitting outside. Someone must have seen them. The last door-to-door team asked locals if they’d seen anything suspicious. This time, just ask people what they saw.’

Barratt piped up: ‘It’s almost seven weeks ago now, Sir.’

‘Yes but it’s not that usual to have a murder on your street, is it Barratt? Even in South London. I call it the JFK Syndrome. Neighbours will remember exactly what they were doing before and after they heard the news. All we need is one person to place Karen at the scene at the right time.’

Shep drove on: ‘Alibi: we have to prove that Karen and her accomplice could have murdered Marion, changed their clothes and made it back to the Pines by six p.m., when she was seen in the car park. I need a team to make that journey at the same time of the evening, several times. Record it in real time on video. We will need to prove that this is possible.

‘Also, get Karen’s main alibi providers in. That’s her sister Laura and the woman they watched TV with between five thirty and six p.m. that day, Bethan Trott.

‘Forensics: I want the fingerprints of everyone employed at the Pines, and anyone who’s worked there in the past twelve months, temporary, agency, contractors, everyone. Cross-reference them against the prints found at the murder scene.’

I felt my head shake. I’d suggested this yesterday morning. We knew that Karen couldn’t have carried out this killing without a male accomplice. Why had we wasted two days before looking for him?

‘I can keep Karen in custody until nine a.m. tomorrow. I’ve already applied for a twelve-hour extension. We’ll only get it if we come up with something new. We need to attack this with all we’ve got.’

Shep walked over to where I sat. ‘We’ll nail her, don’t worry about that.’

‘Thanks, Guv,’ I said, and I meant it.

‘Now I want you to draw up a comprehensive list of why we shouldn’t link Marion’s murder to the Bisset case. I’ll have the Commissioner on the blower first thing tomorrow, as soon as he’s read the papers. Make sure I’ve got enough ammo to buy us a couple of days.’

Before convincing the Commissioner, I had to satisfy myself that Marion’s killer hadn’t struck again and murdered the Bissets.

As I sat down at the computer to compile my list, the warnings I’d fended off rang through my mind.

If it’s domestic, why did he attack her on the stairs?

Speak to any pathologist, they’ll tell you the most stab wounds they’ve ever seen in a domestic is ten or twelve.

Perhaps Fintan and the Big Dogs had been right all along: there’s no way Peter and/or Karen would have stabbed Marion forty-nine times – even with an accomplice.

On top of that, the odds that there were two knife-wielding maniacs on the loose in South London capable of butchering female strangers in their own homes seemed remote.

If, somehow, I’d missed Marion’s Lone Wolf Killer in the ‘unsolved stranger attack’ paperwork, and he’d gone on to kill Samantha and Jazmine, I’d quit the force right away. I saved for another day the imponderable matter of how I’d live with the guilt.

Before that, I’d have to deal with the shame. The media – no doubt exhaustively briefed by McStay and Barratt – would hammer the team and annihilate me. I’d read enough of Fintan’s toxic, hysterical prose to know how he’d garner maximum public outrage.

Blundering cops left a maniac knifeman free to slay a mother and her four-year-old daughter when they missed vital clues from his previous attacks …

… Despite warnings from an eminent forensic psychologist that a Lone Wolf Killer was on the loose, the investigating team tried to frame a twenty-five-year-old trainee nurse with no criminal record …

… An insider today revealed that a junior officer – Acting DC Donal Lynch – missed several clues that pointed to the triple killer …

I had to hope Shep was right. And I needed to provide as many compelling reasons as possible to make the Commissioner believe us. If I could show him significant differences in the modus operandi of each crime, he’d realise that there had to be two killers, however improbable.

Soon I had scraped the barrel and come up with a list, which I wrote out in large hand on a clean sheet of paper.

• Samantha Bisset’s killer(s) attacked her as soon as she opened the front door. Marion Ryan had let her killer(s) inside her flat, which suggests she knew her killer(s).

• Samantha Bisset’s killer(s) spent a considerable amount of time fastidiously dismembering her body before leaving the scene. Marion Ryan’s killer(s) carried out a frenzied attack which lasted between two and three minutes, then fled.

• Jazmine Bisset had been sexually assaulted. Samantha Bisset had been genitally violated with a knife. Marion Ryan had not been sexually assaulted or genitally violated.

That was the best I could come up with. I might as well have written: ‘He didn’t rush so much the second time.’ I placed my handy, bite-sized, exaggerated bullet points on Shep’s desk: I would have felt less grubby squatting over it and taking a dump. Guilt and doubt gnawed away at me, eroding what little bottle I had left.

I exited the station into the hum of a warm summer night. As I turned into Lavender Hill, a sudden guttural grunt startled me.

‘Cheer up pal, it might never happen,’ said a drunk in a doorway.

‘It happens all the fucking time, pal,’ I said wearily, flicking him a pound coin and wondering why they always seemed to be Scottish or Irish.

‘Yer still here though, aren’t ya?’

I had to smile: today’s events had pretty much stripped me down to that level of existential optimism.

As I turned onto Trinity Road, it hit me like a brick in the face. Today I’d attended a double murder scene. The spirits of Samantha and Jazmine Bisset would come to me tonight, for sure. At that precise moment, I wanted to be dead. I’d never felt like that before.

Chapter 30

Trinity Road, South London

Wednesday, August 14, 1991; 21:00

I got back to the flat, forced the front door open over the junk mail we never picked up, and smelled cleaning products. Confused by the gloom, I crept cagily into the shadowy sitting room, sensing someone inside. The irrational part of me feared that the Bissets were already waiting.

Slowly, my eyes adjusted to register a pair of candles glowing above a table set for two. The romantic mood failed to soothe my gnawed nerves.

‘Is that you, Donal?’ Eve called from the kitchen.

‘Yeah, wow, what’s all this?’ I said, feeling unsettled, wrong-footed.

She walked in with a bottle of wine and two gleaming glasses.

‘I’ve cooked you dinner, just to say thanks for letting me stay.

‘Here,’ she handed me the uncorked bottle, ‘it’s one of your favourites. I made a note when I threw out all your empties.’

I wondered what else she’d made a note of. I couldn’t figure out why her efforts had set me on edge: I said she could stay for a few nights, not assume the role of Woman of the House. I hoped to Christ that Aidan hadn’t planned to come home tonight.

She returned to the kitchen as I filled a glass to the brim, downing half of it. ‘Shall we pretend it’s 1988?’ I said, to no one in particular.

I sat at the table as she carried in two steaming oval plates. As she placed one in front of me, I registered her low-buttoned white blouse and scarlet lips. She teetered back to her side, giving me an eyeful of her short, tight black skirt and strappy heels. Had she remembered my thing about waitresses?