‘They explain that Peter has asked them to bring some pots from the house to the Pines – they’re too big for him to carry on the train. Remember, according to Peter and Karen, that’s the reason she drove him back to the house that night. Peter may have mentioned this to Marion that morning, to prime her. Marion lets them in. She picks up her post and leads them up the stairs to the flat. On the landing, one of them stuns her with a blow. She falls. They go to work.

‘According to the pathologist, the attack took two to three minutes. They change out of their bloody clothes, leave the house, get back to the car and return to the Pines old people’s home where Karen is seen just after six.’

I wondered if I was the only one not buying it. Either way, Shep kept selling.

‘Was Peter involved? I think that’s the toughest nut to crack right now.

‘Check out Karen and Peter’s bank and phone records. Get back to the Pines. We need to look at their precise movements on the day of the murder again. Who saw them and at what times exactly? Check out if anyone working at the Pines or anyone employed there in the past twelve months has form for violence. Also find out if any of them has a martial arts belt. Remember, Marion was knocked out by a karate-style chop.

‘The first thing I was told when I joined this investigation was that both Karen and Peter have watertight alibis. But do they? Have we really challenged those alibis rigorously? I don’t think we have,’ said Shep, resisting the temptation to leer at McStay and Barratt.

‘I want them both brought in for interview. Get Karen in first. With Bethan’s revelations, we can really shake her up. I think she’s our prime suspect. Mulroney and Gibson, oil the thumbscrews. Lynch, help them prepare for the interviews. I want nothing short of a full confession from her about the affair with Peter, then a full confession to the murder of Marion. It’s her time to bleed, understood?’

Chapter 23

Clapham Police Station, South London

Monday, August 12, 1991; 11:00

Before I did anything else I had to look through Peter and Karen’s first statements. What if I’d missed something?

I printed out both, along with the lengthier versions they gave later, laying them side-by-side for inspection.

Peter didn’t appear to make any factual contradictions in either. However, I noted a few potential banana skins. How convenient that he’d forgotten his chequebook when buying the fish feed and water cleaner that day. A dated, timed and signed IOU seemed almost too good an alibi to be true.

He’d made other claims that sounded distinctly like arse-covering exercises – or attempts to direct detectives down the ‘stranger killer’ route. He thought Marion had been wearing a bracelet on the morning of her murder that he hadn’t been able to find since. She phoned him at work that afternoon to say she had to run an errand and would be a little late home. He couldn’t remember what that errand was.

Firstly, if Peter wasn’t getting home until nine p.m. – three hours after Marion – why would she bother telling him this? Secondly, while I was no sugar-hearted sentimentalist, I’d have recalled, stored and treasured every single word of the last conversation I’d ever held with my murdered wife, even the details of her trivial errand.

Of course, in neither statement did Peter mention that he and Karen had once been lovers. Mind you, DS Glenn’s blinkered and misdirected team hadn’t asked him.

None of this was proof, though.

As I read through Karen’s statement from the night of the murder, my eyes seized upon a paragraph.

The journey to Sangora Road took no more than fifteen minutes. We drove into Sangora Road and I parked up next to the pub at the bottom of the road.

I grabbed her later statement and located the paragraph I was looking for:

The journey to Sangora Road took fifteen minutes at the most. I couldn’t park on Sangora Road because it was already full. I had to park on the side road. I don’t know what it is called.

My mind flashed back to Friday night: the blazing heat, those visions of Marion, first near the pub on Sangora, then on Strathblaine Road. My guts knotted tight.

Was Strathblaine Road the side road Karen had been referring to in her second statement? And why had she changed her story? I checked an A to Z. Strathblaine Road is the only road off Sangora that you can park on. So that part must be true. So why did she say she’d parked near the pub on Sangora in her first statement?

And then it struck me: what if Karen Foster hadn’t made a mistake? What if she’d been to Sangora Road twice that day? When she first came to kill Marion, she parked near the Roundhouse pub on Sangora Road. This location offered her a grandstand view of Marion’s front door and the top of the road. I’d been near that pub at about five thirty p.m. on two occasions: there were free parking spaces both times. When Karen returned later, at nine p.m. with Peter, there were no spaces left on Sangora. Strathblaine Road has houses on one side of the street only – the other side falls away to railway tracks leading to Clapham Junction station. But it has parking on both sides of the street. There were always parking spaces available on Strathblaine Road.

My shaking finger dialled Shep’s number. I haltingly told him about the differing statements.

‘So? She forgot where she parked. I mean that’s an innocent enough mistake, isn’t it?’

‘Maybe it’s not a mistake, Guv.’

‘I don’t follow,’ said Shep.

‘Maybe Karen parked her car in that area twice that day.’

Shep was silent, then: ‘My God, you’re right. You’re right!’

‘It’s not evidential and, of course, she’ll say she just made a mistake.’

‘Yes but we know better. And this puts her and her car in two very specific places at two very specific times. There have to be witnesses who saw her getting in and out of the car between five thirty and six, especially if she parked near the pub.’

He sounded stoked. ‘Make sure you tell Mick and Colin. Good work, Lynch,’ he said. I basked in those final three words long after he’d slammed down the phone.

But as the glory faded, an eerie chill sent spiders scuttling up my spine: Marion had appeared to me on both those streets. Had she been making sure I picked up on this discrepancy?

‘Sleep paralysis, my arse,’ I said, dialling a phone number.

Chapter 24

Falcon Pub, Clapham Junction

Monday, August 12, 1991; 19:00

That evening at the Falcon I leafed impatiently through a copy of the Evening Standard, but none of it could distract me from the news I was about to impart.

‘Wonderful concept, but highly improbable,’ was how Lilian had laughed off the idea that Marion was coming to me from beyond the grave with clues. Well, how could she explain my twin daylight visions of her, and the fact that it had proven critical to the case?

I’d never bought her sleep paralysis theory. Even though I craved a diagnosis, I resented her desperation to hammer square peg clinical conditions into the uniquely shaped hole of my experiences.

I’d hatched a plan to tell her about the dual-hallucination first, without mentioning its relevance. I’d let her explain it away clinically; then hit her with the fact that Marion’s spirit had directed me to a critical clue. I couldn’t wait to see how she’d go about applying pragmatic science to this inexplicable development.

Lilian crept tentatively through the door: clearly not at home in a pub. After much deliberation, she settled on a white wine spritzer. Thankfully, the barmaid knew what this was.

‘How have you been Donal(d)?’ she asked, back to her original mispronunciation. ‘Look, I know you weren’t entirely convinced by my prognosis, so I got hold of two books, both written by eminent professors who specialise in sleep paralysis research.’