He keyed something into the control panel, waited a moment, then tried again. Outside, at that instant, one of the enforcers was handing his grenades over to Silberman. Var did not understand the reason until the same enforcer picked up one of the assault rifles, removed its ammunition clip and ejected the shell from the breech, then stepped over to the bulkhead door and balanced the tip of the barrel against the floor. Letting it go, he leapt back so the weapon toppled against the door. They’d obviously assumed this door might be electrified too.

‘Fuckit,’ growled Lopomac. ‘Fuckit!’

‘What is it?’ she asked.

‘Pump’s fucked.’

He started working a handle back and forth till the hatch doors began to bulge downwards and, with a clonk, the seam opened. He tried the panel again, and this time was rewarded with the familiar hum of a hydraulic pump in action. Slowly the doors continued hingeing downwards.

Immediately outside the bulkhead door below, the same enforcer tentatively stepped forward and tried the manual handle. The handle crunched over but, with the weight of the forklift pressing against it, the door would not lift from its seals, and therefore could not swing aside on its upper pivot. The enforcer drove his boot against it, but the door moved not at all.

Var turned her attention elsewhere – time to move.

She reached up around the rim of the hatch and, aided by the low Martian gravity, easily hauled herself up on to the roof. Carol pulled herself up almost simultaneously, with Lopomac immediately behind her. After they unclipped their climbing motors, Lopomac reattached the piton gun to the length of rope he had hung from and flicked over a switch on one side of it. This transmitted a low current to the pitons, operating micromotors inside them so as to withdraw their barbs. After a couple of tugs, he hauled up the ensuing tangle of rope and pitons. Meanwhile Var rechecked her visor screen, seeing all but one of the enforcers retreating along the corridor. The remaining one placed a grenade beside the lower rim of the door, then retreated too.

‘Hurry!’ she urged.

Already at the external console, Lopomac first keyed in the instruction to close the hatch doors, then grabbed the external manual pump handle and started to work that too. Slowly they began to close up – just as the grenade detonated below, causing the roof to jerk up underneath them. Smoke instantly filled the corridor, so it took a moment for Var to check if the grenade had been successful. Fortunately it had not, and though the door itself was bent inwards at the bottom, there was not enough room for anyone to slip through.

‘That’s got it,’ said Lopomac, as the hatch finally sealed shut.

‘You go on,’ said Var, gesturing Carol over to the dust cowling along the edge of the roof. She herself began crawling on her belly towards another section of roof.