I will fill you in on the whole story when I see you. Peter tells me Karen’s off to Ireland in a couple of weeks for a weekend. I’m saying nothing until she’s gone. I hope I don’t sound bitter and twisted.’

Shep let it hang and slowly folded up the paper. McStay asked to see it.

‘Now, who can say that Marion didn’t have an enemy?’

No one breathed.

‘I rang Andrea last night. She told me that Marion felt that Karen was obsessed with Peter, and constantly trying to involve herself in their lives.

‘This letter suggests to me that Karen was the third person in their marriage. Marion was “saying nothing” until Karen went to Ireland for the weekend. What did she mean by this? Was she about to confront Peter about his affair with Karen? This has to be our focus now.’

Murmured agreement: he was winning them over, some at least.

‘Tomorrow, I want you to split into four new teams – I’m breaking up your partnerships just for a few days, freshen things up a bit – and I want you to focus on Peter and Karen. Were they once an item? Was he sleeping with her? Was Karen, as Marion’s closest friend Andrea has expressly stated, obsessed with Peter Ryan?

‘I want one team to go back to the Pines old people’s home where Peter and Karen worked. If anything was going on between them, at least one colleague will know.

‘Karen’s people must know if she has a thing with Peter, either now or in the past. I want a team to talk to her family, friends, ex-boyfriends.

‘Another team can do the same with Peter: talk to everyone he’s ever known in London. Was he or is he a player?

‘And finally,’ he said, looking at McStay, ‘I need you to take on the toughest job of all. Go back to Marion’s family and find out what they know. Marion must have talked to someone about why she disliked Karen. She wasn’t the disliking kind. Something was up.’

McStay wasn’t buying it.

‘Are you telling us, DS Shepard, that we’re now focusing solely on Peter and Karen? Based on one undated, half-written page of girlie gossip?’

Shep looked at him, confused. McStay held up the note and decided to spell it out.

‘She doesn’t actually state here that she suspected Peter and Karen of having an affair. She says nothing of the sort. There’s no anger or suspicion, just irritation. I’ve heard worse in the staff canteen. And I trust you’ve read the pathology report. No woman could have carried out this crime.’

‘No, but a woman and a man could have,’ said Shep.

McStay refused to budge: ‘They have solid alibis. Both of them. You clearly have some sort of personal grudge against Professor Richards. I think that’s why you’re ruling out the stranger theory. Well, what if her killer strikes again while we’re looking the other way? The wrong way?’

I had to agree with McStay: Shep wanted to prove Richards wrong so badly that he’d donned blinkers. I’d seen Peter and Karen the night they found Marion. Both had been deeply traumatised and clearly in shock. You can’t act emotions like that.

Shep changed key: ‘I’m not ruling out the Lone Wolf Killer theory, McStay. I just think it’s about time we eliminated the most obvious suspects in this case once and for all. That’s Peter, her new husband and Karen, her husband’s work colleague and friend whom Marion clearly disliked. As for the stranger theory, I happen to think that needs a fresh pair of eyes. That’s why I’m putting DC Lynch on it.’

‘What?’ I stopped myself from saying.

McStay turned and looked at me: ‘You’re giving this to the new kid?’

‘He’ll liaise with Mulroney and Gibson. That’s why I’ve brought them in. Sometimes fresh eyes see new things.’

McStay turned back, still shaking his head.

‘Guv, you said you want us to get on with this tomorrow. What about today?’ asked one of the younger DCs.

‘Ah, yes, this afternoon we’re going on a team-building exercise.’

Groans all round.

‘To the pub,’ Shep smiled. Everyone looked around in confusion.

‘I’m serious,’ said Shep, ‘you’ve all been through the wringer. I think we need to finish our chat over a few pints.’

An hour later, among the cut mirrors, etched glass and faded Victorian grandeur of the Falcon near Clapham Junction, opinions and gossip vied for air supremacy with thick cigarette smoke. I wondered if policing was the unhealthiest profession in the world, maybe even elbowing out journalism in the wheezy sprint to early death.

Privately, some of the officers told me about the ‘Big Dog’ culture of DS Glenn’s team. They all felt that Peter Ryan hadn’t been properly investigated. But the pack leaders – DS Glenn, the Professor, Barratt and McStay – had ruled out Peter and Karen from day two. I’d pass this on to Shep later, though he probably guessed as much already.

Shep got stuck into McStay, Barratt and a real ale chaser. He tirelessly reassured them that the Lone Wolf Killer line of enquiry remained open and live. Within a couple of hours, he had them rolling on their backs.

As drink took hold, more damning claims emerged about Peter. Officers said he ‘loved himself’. The only woman on the investigation team – a brunette who looked capable of taking any one of us in a fist fight – swore he’d flirted with her.

‘I mean, his wife’s barely cold. What a slime ball,’ she gasped. Within a week of Marion’s murder, Peter had emptied both her personal bank accounts and got a refund on her annual rail ticket.

‘Disgusting,’ said Shep.

‘Shows what a ruthless bastard he is,’ said someone else.

I decided to join in: ‘Well, I suppose it’ll tide him over until her life insurance pays up.’

That got a good laugh.

‘Actually that’s a good point,’ said Shep, ‘have we checked whether he gets anything for her death?’

The silence told us no one had bothered. I couldn’t believe it: life insurance, one of the oldest motives in the book. Shep and I exchanged a fleeting look of disbelief. But we needed to win the team over today, so said nothing.

I was taking a leak when Shep came crashing in. He checked the cubicles, then stood at the latrine next to me: ‘Did you see that Scottish git’s face when I read out Marion’s letter? Can you believe he demanded to see it?’

‘He just can’t accept that they messed up, Guv.’

‘Well done on finding it, Donal. Otherwise we’d never have persuaded them to target Peter and Karen.’

‘No problem, Guv. You’ve definitely got them onside now, most of them at least. The junior officers are saying they never felt Peter had been properly looked into. But they were overruled.’

‘That’s good to hear. Honestly, the day you stop listening to other opinions and ideas, you’re no longer a manager but a tyrant.’ I recalled Fintan’s description of Shep as a dictator. He seemed the opposite to me.

‘Of course he’s right in one way,’ said Shep, shaking his cock vigorously, ‘the letter tells us nothing on its own. We still don’t have one solid piece of evidence. Someone will have to cough tomorrow.’

I waited so that he could wash his hands first.

‘Guv, about me looking for connections to other stranger attacks,’ I started, ‘I do worry that maybe I lack the experience …’

‘Nonsense Lynch, it’s common sense. If anything catches your attention, flag it up to Mick and Colin,’ he said, shaking his hands and ignoring the dryer. He looked at me and read my anxiety.

‘Come on, these fuckers spent four weeks looking for a Lone Wolf Killer. I’m not expecting you to find one because there isn’t one. I just have to keep McStay onside. You can be sure he’s reporting back to Glenn who’s reporting back to the Commissioner. You’ll do fine, Lynch.’

He left me drying my hands and hoping to God he was right. If not, some maniac slasher was roaming London unchecked, seeking out his next victim.

Chapter 19