One of two shafts that went down through L3, the ‘Endless Stair’ was a narrow magma conduit within a wider granite chimney. Despite the name, it had no steps down, not even a series of ladders, and the turbines were impassable without a full maintenance team. Which we don’t have.

  The second shaft down was better, though not by much. The well in the floor was circular, smooth-sided and ineffably deep. A thick chain rose from the middle of the hole to a gigantic spool high ahead, next to the metal box of an electricity turbine. The other unseen end of the chain was tethered to a colossal concrete cylinder, suspended unseen in the depths below.

  The shaft used by the gravity-battery descended far into the earth, to L3 and beyond, but it wasn’t a simple thing to lower soldiers down. First, the ponderous weight needed to be lowered the hundred metres to L3, because it wasn’t easily bypassed. Second, the team didn’t have a line long enough to get that far safely.

  All we really have is the great greasy chain the weight hangs from.

  Naturally Sly wanted to discuss the idea with a free climbing expert but where could he find one of those, in the middle of Antarctica?

  Sergeant Eli Brown looked with great interest down into the lightless pool at his feet, his sun-bleached light-brown hair moving from the light breeze rising out of it. The stretched chain, lit by two lamps and a flashlight, didn’t move an inch even when Eli shoved with a mop handle. The titanic weight below didn’t allow the chain to shift. It might as well have been a solid pole.

  Or, rather, the chain wouldn’t give this close to the turbine, Sly thought. Moving the pendulum is a perilous possibility nearer to the weight, a hundred metres down.

  “Lowering the weight wasn’t a problem,” said Trap Singh, shirtsleeves rolled up to his biceps. “The work of five minutes, and three months surplus energy lost. But we’ve no sledgehammer. By the time Eli here manages to break through the wall to L3 with the toys we do have, it’ll be time for the next ice age.”

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  Without asking, Eli reached over to his fullest extent and grabbed the thick, rust-brown chain. In a lithe and effortless motion, he jumped from the side and wrapped his legs around the slimy links. The climber had dressed for the occasion: rubber climbing shoes that showed the shape of his toes, a form-fitting long-sleeved shirt, and a bag of climbers’ chalk. After a short hesitation, Sly let Eli go.

  Eli didn’t care, to him it was a stroll in the park. He eased himself down the thick oiled chain with the grace of a circus acrobat, quickly disappearing into the ink-black pool in the floor. In another thirty heart-wrenching seconds he was back, pulling back up smoothly and without strain. In forty seconds, with help from Sly’s reaching hand, he stood where he started.

  “It’s do-able,” he said, a small smile on his tanned face. “I want to do it.”

  The second time he went over the edge Eli carried a small backpack and a bunch of other things, including a Sig and a headlamp. Wearing shades built into M Frames, his descent was captured for everyone to see, smooth and fast – so neat and tidy it would be worth watching on replay. Eli didn’t carry any kind of hammer, saying it was way too soon for that. He wanted a good look at the end of the chain and to climb all the way back up.

  Sly snorted. He wants the chance to climb the chain twice.

  Eli took about ten minutes to reach the flat top of the vast cylindrical weight, where he rested his feet. Sly reckoned that if a hundred-metre ladder had four rungs per metre set a comfortable distance apart, and if a climber took a step per second, it would take about seven minutes to cover the distance.

  Eli Brown took ten, but without the ladder.

  “Houston, we have a problem,” Eli said easily, no strain in his voice. Sly squinted at the feed but couldn’t see what had given him pause, until he switched from UV to night-sight. Hanging a little above the flat bright top of the cylindrical weight, a black-on-grey patch showed against the wall, one that shouldn’t have been there. The shape was about two feet high by a foot wide, with rugged edges, as though someone had roughly banged out the shape without much care.

  That window in the rock wasn’t smooth, neat or tidy. Not at all.

  “That hole? The one you wanted me to make?” Eli said. “It’s already here.”