Without having seen one before, Ansell knew what it was.

‘It’s a fire-break!’

MacConnachie looked at him and roared with laughter.

Of course. That was why. The pilot wanted to keep them pegged in that part of the field that was ablaze. But there was more to it than that. There must be a gap. One end of the fire-break was still open, the cordon was incomplete. But which?

With the roaring and moaning of the flames growing steadily in volume at his back, and the sky dark with smoke that fled from them towards the river, MacConnachie struggled with the unaccustomed process of reasoning. The patrol that had started the fire would progress up the right flank; they must have reached the fire-break by now, and they couldn’t afford to ignore it; therefore some of them at least had turned down it. Therefore it must be the left flank that was open.

The helicopter had come right down low now, the pilot stolidly waiting their move; MacConnachie could see the observer quite clearly as he talked rapidly into his mouthpiece, and the pilot leaning forward, peering at him, consumed perhaps by a similar curiosity, wanting to know the face of the man whose tenacity matched his own. MacConnachie grinned, raised two fingers in obscene salute, and shouted to Ansell, ‘Come on!’

They splashed through the shallow sludge of water and mud, slopping their way over to the next wall of stalks, and, turning along it, began running down the break to their left. MacConnachie held his gun at the ready.

The helicopter reacted at once, pulling sharply back along their line of flight, coming in fast and low from behind. The next moment they were caught again in its buffeting down-draught and then, as the chopper rose away from them, a tiny cluster of tinsel-bright objects fell from it. MacConnachie seized Ansell’s arm to be sure he saw them and, as they both came to a skidding halt, dropped the case and brought the gun up to his shoulder for three quick shots, tight together, in an attempt at a sudden kill. It failed. The machine rose up unharmed, and a startling clang came back to them as one of the bullets spread itself against a rotor blade and spun off noisily.

The next instant, a barrier of piercing light flowered across the break in front of them as first one, and then two more phosphorus grenades exploded not a dozen feet ahead. An intricate pattern of fern-like structures leapt into the air, dazzlingly etched in pure white smoke, and the vituperative hissing of chemical discharge pitched back at them from the enclosing walls of stalks.

‘Round the side – we can’t go through – it clings like a bastard!’

MacConnachie plunged into the new field at his right, aiming to work his way round the furious active area of phosphorus, and emerge on the far side of it. Ansell followed. The helicopter was turning back.