Saturday, 18 October

The first killing frost of the year struck on the night of the first of October; then, the following day, the skies cleared and the sun rose, burning off an autumn mist which clung to the beaches. Thermometers began to climb into the sixties, and then the seventies as a classic Indian summer took hold. For eighteen days in a row the noon air crackled with heat and electricity along the north Norfolk coast and thunderclouds billowed at sea, mushrooms of boiling, billowing, humid air. Thunder rumbled and jagged lightning crackled, but the rain held off. Trippers and second homeowners made the most of the heatwave for a week, then two, until even they had to go back to work, leaving the sands to grey-heads and couples with pre-school toddlers. The locals simply waited for the weather to break. The water was green and choppy, white with spray: a winter sea under a summer sky.

DI Peter Shaw sat on the back terrace of the Old Ship Inn – one of the coast's burgeoning collection of gastropubs – looking out over Brancaster Marsh, his wife, Lena, beside him. They sat in wicker chairs beside a glass-topped table, a bottle of white wine in a chiller. The plate before Shaw was porcelain, the two scallops chargrilled, each with its accompanying orange 'coral'. The detective used his knife to separate what he knew to be the mollusc's brightly coloured ovary from the rest of its body. There was something visceral about the vivid flesh which made his throat contract. He concentrated on the three new potatoes, which had been shaken in lovage, and the sprig of green samphire, the local 'sea asparagus', picked from the marsh and dusted with sea salt.

High tide was an hour away, and the sound of the surf breaking on the distant, unseen beach was a clear, methodical drum roll. The channels and creeks of the marsh were filling up to the brim like silvered mirrors. Lightning flashed once out at sea and the cutlery and glasses pulsed, as if intermittently charged with neon.

'God's fireworks,' said Shaw. The detective had a quiet, musical voice, which suggested an ability to hit a note at will. One of his eyes was blue – almost colourless, like tap water falling. The other was blind, the iris simply a moonlike white disc. Shaw pressed both eyes tightly shut and saw the forked lightning shape behind the right lid only. Five years earlier he'd been blinded in an accident involving toxic waste on the beach, but he never tired of testing his disability, pushing his remaining senses to the edge of what was still possible while monitoring the performance of the one vital remaining eye.

'This weather,' said Lena, stretching out long, lean legs. 'Can you promise me it'll be like this every year?'

'Sure. Every year. No problem.'

Lena was Jamaican, her black skin glowing after a summer spent working on the beach. The English weather to her was a constant source of real horror. Rainy days in June and July clouded her mood; a long grey English winter left her depressed. Living on the north Norfolk coast had always been a gamble. Sometimes she wished she'd never taken the risk.

'Odd term: Indian summer,' she said. 'Colonial, I suppose – another echo of the Raj?'

'For once you're wrong. Not everything's about the Empire,' said Shaw.

The coast, its moods, its shifting atmospherics, was one of his obsessions. Lena imagined him researching online, worrying away at the origins of that odd couplet: Indian summer.

'Nineteenth century, I think, from the Great Plains of America. A Red Indian summer, do you see? Not very PC. It gets worse: the Indian summer usually followed a Squaw's Winter – that's the first frost. We used to call it a St Martin's Summer – the feast day's November the eleventh, so presumably it can last till then. It's good news wherever you're from, because it shortens the winter. Less months to eke out the harvest grain. We love it because it lengthens the summer.' Shaw scratched his skull through close-cropped fair hair.

'You're telling me we could have another month of this sublime weather?' she asked. Lena's face was made up of a series of ample curves, as was the rest of her. Shaw thought she resembled an animated African mask, like the ones hanging in a museum of ethnology: Lena didn't so much show emotions as broadcast them.

Thunder rolled, buffeting the tables, making the wine glasses and cutlery tinkle. A woman sitting further along the terrace on her own let out a cry of alarm. Each table had a gas heater like an industrial hairdryer set to one side. Several were on, the flame-heated elements glowing like coals, giving an illusion – if little else – of extra heat as the afternoon waned.

'Here's to table heaters and global warming,' said Lena, lifting her glass. 'That's one thing we can do without.' She touched the metal stanchion of the heater beside their table. 'I'd prefer to see our customers wrapped up. We could provide blankets – I've seen that done. Tartan. How about open fires, in braziers? The Plough does that. A bit of heat, but it's a psychological trick. You just feel warm if you can see flames.'

Lena ran a beach café on a stretch of sand between Old Hunstanton and Holme, five miles to the west of where they sat. They'd bought the Old Beach Café for £8,000 six years earlier, having fled London. There was no mains power, no water, and no vehicle access except along the sand in a 4×4. Beside the café was the Old Boathouse, and behind it a small cottage. They'd converted the boathouse into Surf!, a shop selling everything from seventy-pence beach windmills to £3,000 wetsuits. They'd taken the café upmarket, symbolized by a gleaming Italian coffee-maker which looked like a vintage motorbike. This last summer, armed with a licence in Lena's name, they'd started staying open late, serving wine, bottled beer and snacks. The gentrification of the East Coast, spreading north from its heartlands in Suffolk, was bringing new money into a local economy which had once relied on old money.

Lena planned a big extension to the café, turning it into a pub and café, maybe even – eventually – a restaurant. She had in mind a beach bar she'd seen in Cornwall one summer's evening, which had been packed with nearly five hundred thirsty, hungry customers.

Shaw wondered what the hell they were doing. They'd moved to the Old Beach Café from the capital because they loved the solitude, the bleak beach, the dunes. And it was Shaw's childhood home – he'd played on that very beach, swum off the wide sands. They'd left the gritty greyness of the suburbs to give their daughter some space to grow. Shaw was happy to help Lena realize a dream – but one day soon he'd have to tell her that hundreds of trippers on his beach at sunset was his idea of a nightmare.

They'd agreed to spend the winter checking out the opposition along the coast, the dinner bills offset against tax. Lena wanted to write a business plan before approaching the bank for a loan. This was their first recce, and Shaw had chosen the spot. He rather hoped Lena would see that the market was already well served and that most customers wouldn't walk a hundred yards for their Pouilly Fumé and Brancaster mussels, let alone a mile of deserted sand. The downmarket outlook was no better, in his opinion. If people just wanted a pint and a packet of cheese and onion crisps they'd want to park by the door, not walk a mile along the beach.

'This is a world record, of course,' he said, skewering one of the scallops. When they'd first moved up from London they'd got six scallops on a plate. Then, very slowly, the number had begun to go down. All the pubs and restaurants seemed to follow suit, enthralled by just how few scallops could qualify as a meal. So far the lowest total on a plate was three. Two was a new north Norfolk world record.

'Needs a posh name,' he said. 'How about a duo of scallops? It chimes with a trio of fishes.'

Lightning crackled again like an old-fashioned flashbulb. Lena looked at her husband's face in the stark, flickering light as he stared out over the marshes: a nomad's face, wide and open, an outrider perhaps of the Mongol horde – broad, tanned, the skin stretched between cheekbones, the eyes always searching a distant horizon.

'I love this stuff,' he said, sucking the salty green flesh off the finger-like fronds of samphire.

'Glad to hear it,' said Lena. 'I checked out the main suppliers online – thirty-five pounds a kilo. Most of it gets eaten on the King's Road, of course. It grows out there ...' she said, pointing at the marsh, '... and costs nothing to pick. That's one hell of a mark-up.'

Her eyes widened and she parted her lips to reveal pearl-white teeth. Shaw could see what those eyes saw: a packed bar, tables on the sand, food being ferried by a small army of staff. He was good at reading faces. His own was immobile – a handsome mask. Poker faces ran in his family. He'd had to learn as a child to read emotion, character or intent into the smallest of mannerisms: the precise invasion of personal space, the retreat of a chin, the mid-focus glance. Peter Shaw had emotional intelligence the way bats have sonar.

Lena's plate held six oysters caught off Brancaster, two miles west. She held each to her nose, breathing in the ozone, before tipping back the shell with a sharp twist of her wrist.

'So when are you going to tell me why we're really here, Peter?'

It had been a struggle to get Shaw to agree to the winter schedule of checking out the opposition. His day job took up most of his waking hours, heading up a CID unit at King's Lynn, the town twenty-five miles along the coast. Getting him 'off duty' was a feat. Oddly, he'd been positively eager to check out the Old Ship Inn.

'Tell me what you see,' said Shaw. He stretched his six-foot-two-inch frame out straight, touching the chair only at his neck and the back of his thighs. An hour sitting down was beginning to tax his nerves. It was one of the dynamic tensions within his character, that the immobile face was twinned with a body which did not sit still. Lena knew he'd be thinking about his evening run now: the straight mile along the beach to the café, the time chalked up on the blackboard in the corridor to the cottage, each one comfortably under five minutes.

Lena, on the other hand, was often still. When she played 'statues' with their daughter, Fran, she never lost.

She tried to concentrate on his question. What did she see? For the first time she studied the landscape. Brancaster Harbour: a maze of tidal channels between islets clogged with weed and reeds, filling up to flood point. In the next hour islets of reed would slip under the surface. Boats at their moorings in the channel were making that unmistakable sound of ropes against masts in the light breeze. Further out, old houseboats lay at angles in the black mud, a few now wrecks, bare timbers exposed like whalebones.

Lightning lit the scene, this time very close. The thunderbolt made their wine glasses jump on the metal-mesh tabletop.

'I see Brancaster Harbour, close to high tide. What do you see, Peter?'

'Crime scene.'

She couldn't keep the disappointment out of her face. Lena had a slight cast in her left eye – an odd echo of Shaw's own moon-eye – and when she blinked the lid occasionally seemed to stick, so that one eye was slower to blink than the other. It could mean tiredness, exhaustion, or a sudden fall in mood.

'Sorry,' said Shaw, spotting the tic.

'It's OK,' she said. 'But promise me we aren't limited to eating out within sight of the latest serious incident on the CID logbook.' They tried to keep Shaw's career – the everyday, sordid, details of it – out of their home life. The A10 had taken them out of London, through the grimy suburbs, precisely to escape the capital and its crimes. Lena had been a lawyer for the Campaign for Racial Equality in Brixton. Between them they'd seen enough of the dark side of human nature to throw a shadow over a host of angels. Shaw was still a copper, but they always hoped they'd left behind the hard heart of crime.

He picked up a sprig of samphire.

'This is a wild crop, OK? There's not many of those left. All of it grows in tidal marshes, all of it between the high-tide mark and the sea. So it's anyone's. As you have discovered, it's thirty-five pounds a kilo online. A year ago it was ten pounds a kilo. Next year – who knows? Supply is pretty much static, demand rising geometrically. Even I can do the math. Fifty pounds? A hundred? Suddenly it isn't something that a fishmonger can just chuck in with your piece of cod, or your scallops, or your mackerel.

'Along this coast there are probably half-a-dozen serious commercial pickers of samphire. It's a secret world. They don't say where it grows. Some certainly don't tell the taxman. Over the years the business has gone from father to son – along with the geography – in here,' he said, tapping his forehead.

'It's not a full-time job, of course. Just one of those little secret sidelines that can keep a fisherman alive, or a poacher, or a shipwright.'

He leant forward and refilled Lena's glass. This, for the monocular, was a real challenge – one of the many skills he'd had to learn since losing his eye. He picked up the bottle and tipped it forward while holding Lena's glass in his other hand, then let the bottle rest on the lip. He raised his elbow to pour the wine.

'There's fifty places like the Old Ship Inn along this stretch of coast alone. All of them want samphire when it's in season. And they're happy to freeze it too. Then there's the smart London restaurants, and the trendy Manchester restaurants, and the supermarket deli counters. It's big business. The inevitable has happened. Someone's moved in, from London.'

Lena looked out over the marsh. The light was fading gently. Sunset would be about six, so they had a few hours left of the day, but the sun was low and the shadows long.

Lena shrugged. 'It's a wild crop – who's to stop the locals picking it? I don't see much mileage in straight competition. It must be down to local knowledge.

You're telling me there's a bunch of cockney wide boys wandering around the marshlands looking for sprigs of samphire? Del Boy in green wellies?'

'Hardly. There's a specialist outfit at Billingsgate – name of Green Gold. They collect all along the Essex marshes, Suffolk, as far as Cromer. But they outsource, getting local collectors on board. This time it didn't work like that. Someone in Lynn – a gangmaster – stepped in and made a better offer. He'd be the middleman, running the local operation and getting the stuff down to London for Green Gold.'

'Chinese?'

'No, a local thug from the Lynn estates, name of Stepney. Known to the police as John Jack Stepney.'

Lynn's post-war estates were full of East Enders who'd moved north out of substandard housing. They were no more inclined than the locals to commit crime; it was just that there were 80,000 of them, and once they'd got to their new homes the port promptly closed, robbing most of them of any chance of making a decent living. The result was the kind of poverty the government's statistics said didn't exist, and crime, often embellished with that nasty urban edge they'd fled London to avoid.

'In many ways this Stepney character is as much an outsider as a gangmaster from Guangzhou. An entrepreneur too, if twice as ruthless. Stepney put on his whistle-and-flute and went down to Billingsgate to make them an offer: he'd meet their targets and he'd get the stuff down to market. Then he looks at his problem: how do I harvest it? There's a Polish club in the North End at Lynn. There's a Polish club for everything but this one's for sea fishermen, not trawlers – inshore small boat-fishing for pocket money. So he pops along and asks how'd they like to earn a few bob running boats along the coast and picking weeds? I reckon he roped in one of the original local pickers to mark up a decent map with the best locations of samphire and to lead them to it, at least on the first trip. The season starts in June. So did they. It didn't help that they just ripped it up. Thing is, you're supposed to snip off the green fronds of the plant and leave the woody stem in the sand.' Shaw made a scissors movement with two fingers. 'The locals have to come back next year. It's a wild crop, but that doesn't mean it can't be nurtured. This lot did considerable damage in the first month.'