She kissed her daughter’s cheek, then tenderly stroked her stiff hair. ‘How are you feeling today, my angel? Other than itching?’

‘Yeah, OK. I’m tired.’

‘I’ve just been to see Dr Hunter. We have to talk about this.’

‘Not right now. I’m like cotchin. OK?’

Lynn sat very still and took a deep breath, trying to control her temper. ‘Darling, that appointment with Dr Hunter is very important. He wants to make you better. It seems the only way we may be able to do this is by giving you a liver transplant. He wants to talk to you about it.’

Caitlin nodded. ‘Can I have my earpieces back? This is one of my favourite tracks.’

‘What are you listening to?’

‘Rihanna.’

‘Did you hear what I said, darling? About a liver transplant?’

Caitlin shrugged, then grunted. ‘Whatever.’

It took just under an hour and a half for the Arco Dee, making a plodding twelve knots, to reach the dredge area. Malcolm Beckett spent most of this time carrying out his daily routine tests of all forty-two of the ship’s audible alerts and warning lights. He had just completed some maintenance on three, the engine room alarm, the bilge alarm and the bow-thruster failure alarm, and was now on the bridge, testing each of the related warning lights on the panel.

Despite the biting, freshening wind, it was a gloriously sunny day, with a gentle swell making the ship’s motion comfortable for all on board. It was the kind of day, ordinarily, that he loved best at sea. But today there was a dark cloud in his heart: Caitlin.

When he finished the lights, he checked the weather report screen for any updates, and was pleased to see the forecast for the rest of the day remained good. The outlook for tomorrow, he read, was south-west five to seven, veering west five or six, with a moderate or rough sea state and occasional rain. Less pleasant but nothing to worry about. The Arco Dee could dredge in a constant Force Seven, but beyond that working conditions became too dangerous on board and they risked damage to dredging gear, especially the drag head pounding on the seabed.

She had originally been built for sheltered estuary work and her flat bottom allowed her a draught of just thirteen feet fully loaded. That was useful for working in ports with sandbars, such as Shoreham, where at low tide the harbour entrance became too shallow for shipping to pass through. The Arco Dee was able to come and go up to an hour either side of low water; but the downside was that she was uncomfortable in a heavy sea.

In the cosy warmth of the spacious, high-tech bridge there was an air of quiet concentration. Ten nautical miles south-east of Brighton, they were almost over the dredge area now. Yellow, green and blue lines on a black screen, forming a lopsided rectangle, marked out the 100 square miles of seabed leased from the government by the Hanson Group, the conglomerate which owned this particular dredging fleet. The land was as precisely marked out as any farm onshore, and if they strayed out of this exact area, they risked heavy fines and losing their dredging rights.

Commercial dredging was, in a sense, underwater quarrying. The sand and gravel that the ship sucked up would be graded and sold into the construction and landscaping industries. The best-grade pebbles would end up on smart driveways, the sand would be used in the cement industry, and the rest would be either crushed up into concrete and tarmac mixes, or used for rubble ballast in the foundations of buildings, roads and tunnels.

The captain, Danny Marshall, a lean, wiry, good-natured man of forty-five, stood at the helm, steering with the two toggle levers that controlled the propellers, giving the ship more manoeuvrability than a traditional wheel and rudder. Sporting a few days’ growth of stubble, he wore a black bobble hat, a chunky blue sweater over a blue shirt, jeans and heavy-duty sea boots. The first mate, similarly attired, stood watch over the computer screen on which the dredge area was plotted.

Marshall clicked on the ship-to-shore radio and leaned forward to the mike. ‘This is Arco Dee, Mike Mike Whiskey Echo,’ he said. When the coastguard responded, he radioed in his position. Working out on one of the busiest shipping lanes in the world, where visibility could fall to just a few yards in the frequent mists and fogs that came down over the English Channel, it was important for all positions to be noted and updated regularly.

Like his other seven crewmates, most of whom had worked together for the past decade, the sea was in Malcolm Beckett’s blood. A bit of a rebel as a child, he had left home as soon as he could to join the Royal Navy as a trainee engineer, and had spent his first years at sea travelling the world. But, like the others on this ship who had begun their careers on ocean-going vessels, when his first child, Caitlin, was born, he wanted to find work that kept him at sea but enabled him to have some kind of family life.

Dredging had been the perfect solution. They were never at sea for longer than three weeks and returned to harbour twice a day. On the periods when the ship was based here in Shoreham, or in Newhaven, he was even able to nip home on occasions for an hour or so.

The captain reduced speed. Malcolm checked the engine revs and temperature gauges, then glanced at his watch. They would be back in phone range of the shore in about five hours. Five o’clock this evening. The phone call from Lynn had left him deeply disturbed. While he had always found Caitlin a difficult child, he was immensely fond of her and saw a lot of himself in her. On the days that he took her out, he was always amused by her complaints about her mother. They seemed to be exactly the same issues that he had had with Lynn too. In particular, her obsessive worrying – although, to be fair, Caitlin had given them both plenty to worry about over the years.

But this time it had sounded even worse than anything before and he felt frustrated that the call had been cut short. And very worried.

He pulled on his hard hat and high-visibility jacket, left the bridge and clambered down the steep metal steps to the gridded companionway, then down on to the main deck. He could feel the sharpness of the winter breeze rippling his clothes as he walked across to get into position to supervise the lowering of the dredge pipe into the sea.

A couple of his former navy colleagues, whom he met up with from time to time for a drink, joked that dredgers were nothing more than floating vacuum cleaners. In a sense they were right. The Arco Dee was a 2,000-ton Hoover. Which meant 3,500 tons when the dust bag was full.

Mounted along the starboard side of the ship was the dredge pipe itself, a 100-foot-long steel tube. For Malcolm, one of the highlights of each voyage was watching the dredge pipe sink out of sight into the murky depths. It was the moment when the ship truly seemed to come alive. The sudden clanking din of the pumping and chute machinery starting up, the sea all around them churning, and in a few moments water, sand and gravel would be thundering into the hold, turning the whole centre of the vessel, which was the cargo hold, into a ferocious cauldron of muddy water.

Occasionally, something unexpected, like a cannonball or part of a Second World War aircraft or, on one nerve-racking occasion, an unexploded bomb, got sucked up and jammed in the drag head – the mouth of the pipe. Over the years, so many historical artefacts had been dredged up from the ocean floor that official procedures had been established for dealing with them. But no guideline existed for what the Arco Dee was about to haul up on this occasion.

When the hold was full, all the water would drain off through openings in the spillways, leaving what was, effectively, a sand and pebble beach in the middle of the ship. Malcolm liked to walk along it as they headed back to harbour, crunching through some of the hundreds of shells that got scooped up, or occasionally coming across a hapless fish or crab. Some years ago he had found what was later identified as a human leg bone, a tibia. Even after all these years, the mysteries of the sea, especially what lay beneath it, filled him with a childish excitement.