Way, way below was a great reef, with coral outcrops, sponges, a kind of blue vault. A crowd of barracuda swam by, there were angel and parrot fish, silversides, horse-eyed jacks. It was a total joy, and Dillon jack-knifed and went down, checking his dive computer for its automatic readings on depth, elapsed time underwater and safe time remaining.

And then, there below, was the freighter, still in very reasonable condition. Dillon turned, made the OK sign to Billy and went down.

He led the way in through a torpedo hole on the starboard side, worked his way through a maze of passageways, emerged through another torpedo hole in the stern and paused. He made a sign to

Billy, thumbs down, and jack-knifed again.

There in the detritus on the seabed under the stern, he hovered and scrabbled with gloved hands and, by a miracle, came up trumps straight away. What he pulled out was a small figurine, a religious figure, a woman with large eyes and a swollen belly.

Billy came close and looked, his expression ecstatic, then he went down himself and started to search. Dillon hovered, then Billy came up with some sort of plate. Dillon nodded and they started up.

Back on the boat, they held their finds out for Hal Stone and stripped off their diving gear. The Professor was delighted.

'Dammit, Dillon, this figurine is a major find. The British Museum would go crazy for it.' 'And what about my plate?' Billy demanded. 'It's a temple votive plate, Billy, and an absolute beauty.'

Billy turned to his uncle. 'There you go. I mean, we've brought up stuff the British Museum would give their eye teeth for.'

'And we've only started, Billy,' Dillon said as he lit a cigarette and turned to Stone. 'We've got visitors.'

Colonel Tony Villiers was a tall, saturnine Grenadier Guardsman in his late forties, many of those years with the SAS. He had soldiered from the Falklands to the Gulf War through countless tours in Ireland. Decorated several times, there wasn't much he hadn't seen, and a tour in Bosnia and Kosovo had compounded it. He sat there in a small motor cruiser now, in headcloth and khaki uniform, a young officer with him, and coasted in to the Sultan.

He came up the ladder and Hal Stone greeted him. 'We've met before. I'm Charles Ferguson's cousin.'

'That's a recommendation,' Villiers said. 'And this is Cornet Richard Bronsby, Blues and Royals.'

'So we're still at it,' Hal Stone said. 'Just like the good old colonial days. This is Sean Dillon, by the way, and Billy and Harry Salter.'

'I know about everyone,' Villiers said. 'Charles Ferguson has been very forthcoming.'

A few moments later, sitting in the stern of the Sultan under an awning, Dillon said, 'And just how much has good old Charles told you?'

'Enough to indicate that he doesn't know what the Rashids are up to, which is why he's sent you and your friends, Dillon.'

'You and I have been close in the past but never met, thank Christ,' Dillon said.

Villiers said, 'God help me, but I spent enough time chasing you all over South Armagh.'

'Ah, well,' Dillon said. 'I suppose we're off the same side of the street. Is Cornet Bronsby?'

'He's just learning.'

'Good, then let's have a drink and see what the Rashids are up to.'

They pulled beers out of a cooler, and Villiers said, 'Paul Rashid is an old comrade. We did the Gulf together, he got an MC. He's a first-class soldier.'

'Who runs this place,' Dillon said.

'That he does. And, yes, before you ask me, there's little doubt that he's responsible for the Sultan's death.'

'So what would you say they're up to? Why do you bring a notorious IRA terrorist and his team to a place like Hazar?'

'Because you want them to kill someone for you, I'd have thought.'

'But who?' Dillon asked.

'We'll have to see. Unfortunately, I can't stay. We've trouble on the Border from Yemeni Marxists, so Bronsby and I must get back and do a little policing.'

'Stay in touch,' Dillon said.

'You can rely on it. Just one thing.'

'What's that?'

'The youngest Rashid brother, George, the one who was a Second Lieutenant with One Para in Ireland? My spies tell me he's up in the Empty Quarter, operating with the Rashid out of Shabwa Oasis. George not only speaks fluent Arabic but the Rashid dialect.'

'Well, good for him,' Dillon said. 'My Arabic isn't too bad. My Irish is perfect.'

Villiers laughed and replied in Irish, 'I had a grandmother from Cork who used to force it into me when I spent school holidays with her. Good man yourself, Dillon. Keep the faith. Here's my mobile number if you need me.'

Dillon turned to Cornet Bronsby. 'Listen to your man here, son, he's the best. You're in bad company up there, so if you want to live…' He shrugged.

Cornet Richard Bronsby smiled, which made him look about fifteen. 'I'd say I've been in extraordinary company, Mr Dillon.'

He held out his hand and Dillon took it. 'Well, as we say in Ireland, watch your back.'

Towards evening, Dillon and Billy decided to dive again. There was still plenty of light, and it was warm and the wind gentle as they drifted in. In the harbour, Kate Rashid sat on the stern deck of an Arab dhow and watched through glasses. Kelly stood beside her.

'Dillon and Billy Salter. They're going down again.'

'What do you want me to do?'

'Kill them now,' she said. 'Take Said and Achmed with you, and I want no slip-ups, Kelly. There's too much at stake here.'

'As you say, Lady Kate.'

Dillon pulled on his jacket with his tank and Billy did the same. Harry and Hal Stone checked their gear.

'Christ, this is great,' Billy said.

'You've got your knife?'

'Of course I have.'

'Then take a spear gun.'

'Why, Dillon?'

'Because sharks are not unknown in these waters.'

'Really?' Billy laughed. 'Well, you learn something new every day.'

Harry said, 'You bleeding watch yourself.'

Billy grinned, pulled down his mask, and went over. Dillon laughed at Hal Stone. 'What was it Suetonius said, "Those who are about to die salute you"?'

'I could give it to you in Latin,' Stone told him.

'Oh, it's the thought that counts,' said Dillon, and went over the rail after Billy.

There was the blue vault again, that strange feeling of space extending all around them, the freighter below. Dillon and Billy went down together, spear guns in hand. They saw barracudas again, and three or four manta rays down on the bottom. Dillon felt good, enjoying every moment as he dived down, Billy following. They went through the first torpedo hole entry, followed each other through the maze of passages, then emerged through the stern torpedo hole… when Kelly plunged down toward them with Said and Achmed, all three clutching spear guns.

Dillon tapped Billy on the back and pushed him away as Achmed fired a spear. It narrowly missed Billy. Dillon jack-knifed, spiralled, fired upwards and caught Achmed in the chest.

Kelly fired his spear and it dropped into Dillon's left sleeve, a glancing blow that did no damage except to rip the material of his diving suit.

Kelly closed, a knife in his hand, and Dillon grabbed for his left wrist. As they wrestled, Said fired at Billy, who swerved to one side and fired in return. The spear caught Said under the chin.

Dillon and Kelly struggled frantically, then Dillon pulled him round and slashed with his knife across Kelly's air hose. There was a great disturbance in the water, bubbles everywhere, and then Kelly stopped kicking and drifted away.

Achmed struggled to pull the spear from his chest and Billy swerved around him and slashed at his air hose. Then Billy hovered beside Dillon and they watched the three bodies sink below them.

Dillon gave the thumbs-up sign and they started to ascend.