He moved quietly forward. The guard was standing just where the tunnel met the meeting point. He had his back to it, and he was leaning against the wall. Whether he was drowsing or alert, it was impossible to say from here. Porter inched out further, his back flat against the wall. The knife was nestling in the palm of his hand. He was gradually adjusting his eyes to the soupy light. He could see the barrel of the man’s gun. An AK-47: the lamp in the meeting point was catching on the gleaming wood of its polished stock. Porter kept moving. He was about ten metres from the man now. He was holding his breath: he knew from his time in the Regiment that it was the sound of your breathing that usually gave you away. The floor was just dust and grit so at least it wasn’t scratching against his trainers. Five metres. His back was tight against the wall, slipping into the shadows, making sure he was virtually invisible against the rock. Three metres. He could see the man’s shoulders twitch. He was a big man, Porter noted: six foot, with hefty shoulders, taking his weight up to two hundred pounds. He could hear him grunt. Or maybe a snore. His hand rose upwards. For a moment, Porter was certain he was going for the gun. All he had to do was look round, and he could spray the space with bullets: Porter would be shredded to pieces within seconds. He tried to melt into the rock. The man picked at his nose, grunted again, then slumped back against the side of the rock. Porter took a step closer, then another. He raised his right hand, and steadied himself. With a sudden, swift movement, he darted forward. He cupped his left hand around the man’s mouth, dragged back hard with all the muscles in his shoulders. He could hear the man starting to cry, but the hand was effectively stifling the noise. He was starting to shudder, and as his muscles absorbed the sudden shock of the attack, he heaved backwards. Porter struggled to contain him. You’ve only got a fraction of a second, he reminded himself. Once you get into a fair fight with this bastard, then you’re a dead man.

In an instant, Porter’s right hand was thrusting towards the man’s neck. The knife pierced the skin, making a neat incision, in the space between the jawbone and the collar bones where a blade could cut straight through to the wind-pipe. Porter had barely a moment, and he knew he had to slice the man open as skilfully as any surgeon: except his purpose was to end the creature’s life, not preserve it.

There was a hiss of air: the unmistakable sound of oxygen wheezing out of a collapsing windpipe, like an old tyre with a puncture. Porter twisted the knife around, letting it complete its deadly work, while at the same time keeping his hand gripped tight on the man’s mouth. He stifled a bolt of pain as his victim summoned up enough strength to bite into the palm of his hand, but that was the man’s last moment of resistance as the life drained out of him. Giving the blade a final twist, Porter made sure the windpipe was completely cut open, making it impossible for any air to get through to the brain. He removed his hand from the man’s mouth, and checked his pulse. Dead. He yanked his body back, lying him down flat on the ground.