For a moment I thought he was going to ask us where we had gone, but he decided against it. He knew we hadn’t gone anywhere. And suddenly he was furious.

‘Resentment killed them,’ he said. ‘Jealousy – this country reeks of it now.’ He put the unlit cigarette back between his lips. ‘Isn’t it bloody obvious? Envy killed them.’

The Officers’ Mess at RAF Brize Norton overlooks the airfield, and from the window I could see a huge fat-bellied aircraft waiting on the runway, its four turboprop engines idle as all around its great bulk men in sleeveless yellow tabards made the last of their checks.

A wide ramp was open under the tail of the aircraft – a Lockheed C-130 Hercules – but the troops in their camouflage fatigues stood patiently on the tarmac, as though waiting was one of the things they were trained for, and good at. The Royal Gurkha Rifles were shipping out tonight.

I watched the faces of the men, all those small golden-faced warriors who somehow looked both gentle and fierce, and far off in the darkness I could see the distant lights of Oxford glinting and glittering in the night. It had only taken us ninety minutes to drive from Savile Row to Brize Norton after the afternoon briefing, but London felt far away.

I turned at the sound of a man’s harsh laughter.

Captain Ned King and DCI Mallory sat facing each other on red leather sofas in the red-carpeted room. Mallory was leaning forward, his face impassive, unsmiling, letting the other man fill the silence. Like the men on the runway, Captain King was dressed in camouflage fatigues.

‘Forgive me,’ he said, grinning broadly, ‘but there’s no great mystery here. Adam, who I hadn’t seen in many years, was a drug addict. And Hugo was a sex addict. These are high-risk hobbies, detective.’

‘But who would want to kill them?’ Mallory said.

‘Off the top of my head? Try Adam’s fellow drug addicts. Try Hugo’s Russian wife – or possibly some of her Russian friends.’

Mallory nodded, as if giving the matter some thought.

‘You really think Hugo Buck’s wife is capable of killing someone?’ I said.

King turned his scarred face towards me. He was not smiling now.

‘I think that anyone in the world is capable of killing someone else,’ he said.

‘But your friends died in exactly the same way,’ I said. ‘All the evidence suggests the same killer. Do you really think that’s just coincidence?’

Captain King shrugged. ‘What I think is that death is random. That’s what I think. And that’s what I know.’

From the back of the mess came the sound of snooker balls kissing. Two officers were laughing easily together.

‘Helmand is the only place I’ve ever seen a man eat his lunch and defecate his breakfast at the same time,’ one of them was saying.