For a start, they would have to identify all the holiday cottages within walking distance of the Light House. Some of them might have been sold in the last two years and converted into permanent homes. More likely, though, the trend would be the other way round. He expected to find a greater number of holiday cottages in the area now than there were when the Pearsons visited.

'Another rented cottage, I suppose?' he said. 'Not one they owned themselves.'

'Oh, I think so. If they owned it, they would probably have visited the area regularly, wouldn't they? Someone would have known them.'

Cooper nodded. In that case, he'd be relying on a property owner with good records, or a lucky entry in a guest book.

'Needle in a haystack come to mind?'

'I don't suppose it was followed up all that well,' said Fry. 'Another lead that was just recorded and written off, I imagine.'

This was what Cooper had been worried about. The Pearsons had been in the Light House the night before they disappeared. That had been picked up by the original inquiry, with all those unproductive witness statements taken from the likes of Aidan Merritt and the other regulars and staff at the pub.

But he was pretty sure the couple had been there the previous evening too, the night of the YFC party. Why had no one ever mentioned that?

Well, it seemed the investigation had only examined the final two days before David and Trisha Pearson went missing, at least in any detail. The SIO might have made a decision not to expend resources needlessly on trying to trace the Pearsons' movements earlier in the week. There was a law of diminishing returns in these things. You could spend more and more time on a particular line of enquiry, allocating more and more resources, but find that you got fewer and fewer returns on the effort. Someone had to make a decision where the cut-off point came.

Still, it was a little bit odd, if the Pearsons had also been present at the Light House the night before, that no mention was made of it anywhere in the statements. Was that actually the case? He hadn't been through the statements himself, so he couldn't be certain. He'd better tell someone now, before things went any further.

'Diane,' he said, 'have you got a minute?'

She raised an eyebrow, but led him back into the little office she'd been allocated.

'What is it?'

Cooper explained to her about the evening at the Light House, the Young Farmers Club, and his recognition of David Pearson.

'A Young Farmers' event?' said Fry. 'You mean prehistoric mating rituals, with extra straw?'

'Something like that,' said Cooper, feeling a flush rising.

'And I suppose a vast amount of alcohol was consumed?'

'I'm afraid so.'

Fry studied him for a moment, a smile playing at the corners of her lips. Cooper rarely saw her break into a smile, and he didn't care for this one. He knew he was the object of her amus.e.m.e.nt, and he found it infuriating.

'From experience, I'm guessing that you weren't entirely sober either, DS Cooper,' she said.

'It was a Christmas party.'

As he said it, he could hear Matt's voice in the back of his mind. You were as p.i.s.sed as a newt that night. If Matt thought he was drunk, then it was certainly true. Fry's 'not entirely sober' was an understatement, for once.

'I just thought it would be surprising if no one mentioned it in the statements taken from the Light House.'

'Due to a communal alcoholic haze perhaps?'

'Possibly. I'll get Luke Irvine to double-check, shall I? He's been going through the files. What do you think?'

Fry had stopped smiling now, which was a relief. He could see her brain working, weighing up the advantages.

'Yes, good idea.'

'I'll get on to it.

Cooper felt a bit more bounce in his step as he went back into the CID room. He had a slightly different view to Fry's, though that was perfectly normal. He wasn't thinking of a communal alcoholic haze on the part of the Light House staff and customers a more of a rather curious bit of collective amnesia.

In fact, the original inquiry had done a surprisingly thorough job of examining accounts of the Pearsons' visit to the Light House. There was an entire file containing statements from staff and customers, and even a sketch plan showing where all the people spoken to had sat or stood in the bar, in relation to the Pearsons. Someone had worked quite hard on that. It must have taken a considerable amount of time to put together. Above and beyond the call of duty, really.

Then Cooper noticed the date on the plan, and realised it had been drawn up some months after the disappearance. He wondered if the date would correspond with some particularly high-profile bit of media coverage, or additional pressure from the Pearson family.

'If only we could understand why Aidan Merritt had to die.'

'Well, it's simple. He must have had incriminating information. Someone needed to shut him up.'

'But why leave it all this time? If he knew something about the fate of David and Trisha Pearson, the chances are he'd known it for the past couple of years. So why wait until now? Did they think he was about to start talking?'

His last question sounded rhetorical, even to himself. No one bothered answering it. Instead, Villiers moved quickly on to the next question.

'And what made him agree to meet the person who killed him? Because that's what must have happened, isn't it? Merritt went to the Light House voluntarily. There could have been no other reason, except to meet someone. The pub had been closed for months. And in view of the fires spreading across the moors, it was a location you'd want to avoid unless you had a very pressing reason to be there.'

'You wouldn't meet a person you were about to incriminate, though, would you?' said Fry. 'That doesn't make any sense. Aidan Merritt wasn't stupid, after all. Do you think he'd agree to a meeting with the one individual who had a reason to get him out of the way? And on his own, in an isolated spot? No.'

'He could have been lured to the pub by someone else,' suggested Hurst. 'Someone he trusted.'

'Conspiracy now?'

'Well, what else?'

'Are we suggesting that Merritt was somehow implicated in the Pearson inquiry himself?'

'Yes, I think so.'

'We've found nothing in his circ.u.mstances to suggest that.'

'The fact that you haven't found anything doesn't mean he was innocent. You can't prove a negative. Not like that, anyway.'

'He was there at the pub on the night before the Pearsons disappeared. We've established that much at least.'

'But we don't have a single witness to suggest he had any contact with them.'

'Where does our chart put him?'

'Down at the far end of the bar, at a table near the games room,' said Irvine.

'He was on his own, though?'

'Sort of.'

'Sort of? What does that mean?'

'Well, he was a regular at the Light House. He knew a lot of people. You know what it's like when you're in your local.'

Irvine looked at Diane Fry, seemed to decide that she might not know what it was like at all.

'Look, we interviewed a number of customers who spoke to Merritt during the evening. He chatted for a while to some old biddy called Betty Wheatcroft. She remembered discussing how badly behaved young people were these days.'

'Old biddy?'

'Yes. Every pub has one.'

'All right.'

'So ... he chatted to Mrs Wheatcroft. At one point Merritt was asked to make up a foursome for a game of pool. They might not have called him a friend, and he certainly seems to have gone there by himself. But he had a lot of acquaintances. He was among people he knew. Some of them he'd known since childhood. That's not the same as being on your own.'

The expression on Fry's face suggested that it might be possible to be alone among any number of acquaintances, but she let it pa.s.s.

'It still seems odd,' she said. 'I mean, no matter how many casual acquaintances he had, it's a bit odd for a man to go the pub on his own just before Christmas and sit at a table by himself, surrounded by crowds of people celebrating, having parties, getting drunk.'

She glanced at Cooper briefly as she made the last remark. It was a very quick gesture, but everyone noticed it, he was sure. Fry didn't always need to say anything to make her point.

'We talked to his wife,' pointed out Hurst. 'She doesn't like going to pubs. She does drink, but says she prefers to stay at home and get a bottle of wine, watch a DVD or something. But she accepted that Aidan liked the company in the bar. He didn't drink heavily, she says. So it was perfectly normal, for him.'

'He didn't drink heavily?'

'No.'

'So he must have been relatively sober on that night. And from his seat near the games room, he would have had a clear view down the bar. Correct me if I'm wrong, but surely he would have been able to watch David and Trisha Pearson from there all evening, without any trouble.'

'You're wrong,' said Irvine.

Fry raised a cool eyebrow at him. 'Oh?'

'Well, you're forgetting something.'

'What?'

'The bar was absolutely packed. It was heaving. There must have been dozens of people between Merritt and the Pearsons, and most of them standing up too. He would have had trouble fighting his way to the bar to get served, let alone continually observing someone at the other end of the room, especially if he was sitting down. It's just not feasible.'

'That's not to say ...'

'All right,' admitted Irvine. 'That's not to say he didn't see something. Like you said, we can't prove a negative.

'Not in that way,' said Fry. 'Not at all.'

'The only thing we can do is make a start on interviewing everyone we know to have been in the bar, and try to cross-match from their accounts.'

'There must have been people coming and going all night. It's hopeless.'

'We need to cover all the ground again,' said Fry. 'But we should also be looking for things that weren't done at the time. If Aidan Merritt had some connection with the Pearsons, we need to find out what it was.'

'How do we do that?'

'Talk to people who knew him. There must have been some at the Light House.'

'We've got the name of a full-time barman, Josh Lane,' said Irvine. 'And a few of the kitchen staff. Then there are the customers Merritt spent time with. It's a short list, though. Vince Naylor, Ian Gullick ... and that's about it. The person Mr Merritt seems to have talked to most is Betty Wheatcroft.'

'The old biddy?'

'That's the one. From her statement, she sounds to be as odd as Merritt. But I suspect as well educated.'

'Kindred spirits, then.'

Cooper surveyed his mental image of the bar at the Light House, managed to locate someone like Betty Wheatcroft sitting in a corner with a gla.s.s of Guinness and a plastic carrier bag. As Irvine had said, every pub had one. He might just be filling in the details from a hundred other old biddies sitting in the corner of a bar, but the image seemed real enough.

'What are you thinking?' asked Villiers.

'I'm thinking that I can see her already.'

'Ben, there's no need to start imagining things. Just stick to the facts. That was always your weakness, you know a you're much too imaginative for a police officer.'

'Thanks for the advice, DC Villiers. I'll bear it in mind.'

Fry pulled on her jacket and turned to leave. Cooper caught up with her and stopped her with a touch on her arm.

'Diane ...'

'Yes?'

'Our tasks are overlapping now,' pointed out Cooper. 'There's no way round it.'

'I suppose so.'

'I realise your DCI has other irons in the fire on the Merritt inquiry a forensic evidence must be producing some leads?'

'Yes.'

'But we could be turning up some equally useful information from our end.'

'Just keep feeding it into the inquiry through me,' said Fry. 'And we'll a.s.sess its value.'

Cooper knew he'd have to accept that. He'd tried his best to get further into the inquiry, but he'd failed. Fry was a brick wall. He'd have to find another way, that was all.

'There's one more thing,' he said.

'Spit it out, then. I've got plenty of things to do.'

'I think you're coming down too hard on Luke and Becky. They're my team. You don't have any right to talk to them the way you do.'