I’ve always been suspicious of men and women claiming to be friends. In my experience, one of them always has some sort of romantic designs on the other. But none of this was proof. None of this provided the fresh plot twist Shep craved. I’d seen the bloodlust in his eyes. I dreaded having nothing juicy to throw his way. He might devour me instead. I had to find something – anything – to impress him.

I asked my frosty new colleague if I could take a look at the exhibits recovered from the murder scene. Wordlessly, he handed me a numbered list, led me to a cupboard, unlocked the door and stomped off. I pulled the door open, my eyes fixing instantly upon the grisly familiarity of Marion’s handbag, jacket, keys and post. A shiver fizzed across my neck, making my shoulderblades rattle.

I reminded myself that these were inanimate objects, nothing macabre, and got stuck in. Soon, all that remained unsearched was the very first thing I’d clapped eyes on in the chaos – Marion’s flowery plastic handbag. It was the usual dumping ground for receipts, make-up, a brush, some loose change. She smiled out at me from a Reuters security pass: demure, poised, gentle – a far cry from the crazed harridan who had been attacking me. I pulled out a tissue with a bright pink impression of her lips. I held it reverentially, this last remnant of her living body, and let a fresh band of melancholy pass through me. Marion’s Turin Shroud. I thought about how much an item like this would mean to her family, yet here it is, stuck in a sterile cupboard, destined for the skip. I knew it would never be evidence in the case, so I folded it carefully and pocketed it: one day I’d send it to her mum Mary.

A small gold zip on the back of the bag revealed a thin compartment. I could barely slide my fingers in. Right at the bottom, I felt something long and thin. More prodding revealed that this object was trapped within the inner lining. I looked inside the handbag again. I noticed for the first time a barely-visible little compartment – lining on lining and stitched in the middle. I tried the small opening on one side and could only get two fingers in. I pulled out the object: a tampon. I realised this was Marion’s secret compartment. There was nothing else on this side of the stitching, so I slid my fingers into the small gap on the other side. I felt a thin scrap of paper. I dragged it up and out.

It was a folded page ripped out of a small notebook. I opened it.

‘Dear Andrea,’ began the undated, unfinished letter, clearly from Marion to a close friend. My eyes popped: the contents of this note changed everything.

Chapter 17

Church Road, London SW19

Thursday, August 8, 1991; 21:01

I hadn’t seen Gabby since intercepting Dom’s deranged love note a couple of weeks back and packing her off to Kent.

Earlier today, she left a message on my home answerphone.

Hi Donal, Gabby here, from Salcott Road, you know the woman men can’t stay away from. Anyway just to say I moved into a house share in Wimbledon on the first of the month with some old friends from Uni. They happened to have a room free so it felt like it was meant to be really. Anyway, thanks for all your help these past couple of weeks. If you could drop my post around some evening this week, that’d be great. If you’d like to call me at work to let me know when you’re coming, that’d be even better because then I can thank you personally and maybe introduce you to everyone. I’ve told them all about you! But don’t worry if you can’t do an evening. Hopefully see you soon.

By the time I got to Church Road SW19 it was already after nine p.m. I couldn’t wait to see Gabby and tell her about my breakthrough today. On the downside, I felt knackered and wasn’t sure I could handle her no doubt highly educated and very chatty friends. These days, I seemed to have about ten per cent of everyone else’s puff.

But her bundle of post included a couple of large packages – books of course – that wouldn’t fit through her post box. I buzzed and reassured myself that I could hold my own with these people if I had to. I’d discovered that my accent acted as an impenetrable shield against what certain English people wanted to do most: pigeonhole you by class and education. It was impossible for them to judge whether I was educated or thick, rich or poor. So long as I avoided the subject, they might not even be able to tell that I’d never been to university.

The door was flung open by a lady with spiky blonde hair who asked me what I wanted. I held up the bundle and explained I was dropping round Gabby’s post. She turned, shouted, ‘Gabby, someone for you’, and disappeared. So much for the hero’s welcome.

Gabby bounced down the stairs in denim shorts over black tights and a tight white vest, all indie rock and beaming. Sharing with Uni friends had clearly made her regress.

‘Evening, Officer. Do please, come in.’

She got to the bottom of the stairs and strode confidently towards me, a new woman. I couldn’t understand why her familiarity made me uneasy: maybe I found it easier to empathise with victims.

‘Well, what do you think of the place?’ she said, arms outstretched. Before I had time to answer, she ordered me to follow. I got the grand tour of a grand old sprawling Victorian family home, complete with wonky chandeliers, oriental rugs, vanity watercolour portraits, a grand piano, vast leather couches, school corridor radiators and a mossy-glassed, off-kilter conservatory.

Robert Johnson played on an old-school record player stained with candle wax.

Her flatmates lounged about with music magazines, red wine, rolling tobacco and Rizlas, clearly determined to test my law enforcement convictions.

‘Hi everyone, this is Donal,’ Gabby announced, and I felt like I’d gatecrashed cool.

The goth girl squeaked: ‘Hello, Donal’ and I couldn’t tell if she was taking the piss.

‘Hi,’ smiled spiky blonde, as if she’d just met me for the first time.

The man – skinny, blonde and more feminine than either of the girls – cut straight to the quick: ‘How would you feel, Officer, about me engaging in some doobie, here in my own home?’

‘That’s Ricky,’ said Gabby, in a manner that suggested everyone else in the world would have known already, ‘he’s a session player.’

‘Rick, is that short for prick?’ I thought better of saying, opting for the more convivial: ‘Yeah you go for it, man. I’m only a bastard on duty.’

That seemed to calm everyone down no end. Before long, I was red-wining them under the table while enduring their stories. I foolhardily took several tokes on several joints – declining to tell them the one about the last time I sampled drugs, you know, when one person died and another ended up in prison.

They were all completing Masters’ degrees or PhDs, had jobs they felt beneath them and no real idea what they wanted to do with their lives. I resisted the temptation to say: ‘Find something you like and just go for it.’

At some point in the night, one of them mentioned Sylvia Plath. When I asked if she was the woman who sang ‘Je Ne Regrette Rien’ they nearly died laughing.

Just as they recovered, I said, a little bitterly: ‘I guess not then.’

They slid like capsized Alps into balls of hysterics: Gabby’s convulsions the most pronounced and cutting of all.

Not wanting to appear petulant, I waited fully five minutes before making my excuses to leave. As Gabby went to grab my coat, friendly goth said: ‘We haven’t seen her laugh like that in years. You’re really helping her come out of herself.’ The others concurred and insisted I come back soon.

‘Any time you like, dude,’ drawled Ricky.

At the front door, Gabby inspected my tatty old coat and asked when it had last been to the cleaners.

‘No gumshoe worth his salt sports a dry-cleaned coat. Look at Marlowe, Sam Spade, Columbo?’