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.

As soon as he got among them, MacConnachie saw that the stalks in this field were, in one important respect, different from those in the last: they grew farther apart. This meant that he could run between them much more easily and quickly and that, since his field of vision was correspondingly enlarged, he could watch most of the helicopter’s movements most of the time. Also the air was notably clearer, the insects larger and less numerous, the danger of choking much diminished.

As the chopper bore down again, coming this time from their front, he looked up and stopped abruptly. The observer was leaning out of the cabin and aiming some sort of weapon at them. MacConnachie raised his own gun but before he could fire the other man discharged and a bright, glowing red ball flashed into the stalks in front of them. It took MacConnachie so completely by surprise that the observer had withdrawn and the helicopter broken off the contact before he could react.