Back above the rock face, Agata fought to maintain her concentration. Twice she chased features in the stone that turned out to be nothing – perceptual illusions, or wishful thinking. It was better to pursue false alarms that to miss a single bomb, but her air supply wasn’t infinite.

Looking back towards the rim she caught a glimpse of another searcher, a lonely silhouette against the blaze of the transition circle. By now there was no way of guessing who it was, but the figure looked safe and busy. It was tempting to exchange a few words, to compare counts, to share strategies . . . but even in its tightest directional mode the link was only for emergencies, so Agata did nothing to stop their drift apart.

The next find was so clear that Agata cursed her stupidity as she formed the triangle; the phantoms on which she’d wasted so much air seemed inexcusable now. As the rock halted, the occulter appeared almost directly below her, but she was surprised to see how different the package looked from the last one.

She moved closer. There were no strings; the bomb was secured to two posts that rose from the occulter’s arms, lifting the rigid assembly clear of the dodecahedral core that held the air jets. But how had these posts been attached, out on the slopes? Was this the occulter that Tarquinia had repaired – and she’d had to perform some strange modifications in the void?

Agata was baffled, but she didn’t have time to make sense of it. She took a wrench from her tool belt and set to work; the jetpack braced her with yet more expenditure of air. She tried to turn the post itself, but it was too smooth and she could get no purchase on it. She groped around the attachment point on the arms, but there was no bolt head. The posts seemed to be glued in place.

She closed one hand around the occulter’s arm then shut off her jetpack’s airflow completely, letting herself hang down across the vertical rock face. She took a flat bar and inserted it between the machine’s arm and the rock, then began trying to prise the splayed drill bits out of the holes they’d made. But however hard she strained there was no perceivable effect; the drills were mounted too securely and the rock itself wasn’t going to crack.

If she’d had more air she could have tried taking the drill assembly apart; she’d put half of them together herself, so she should have been able to reach in and unscrew all the same bolts by touch alone. But not while she was clinging to this sheer drop. She took a high-powered coherer in her free hand and began carving through the posts that held the bomb in place.