Tarquinia pushed a button on the remote control and the occulter rose from the floor. The core of the tiny craft was a dodecahedron about a span wide, with air nozzles fixed in the centres of eleven of its pentagonal faces. Attached to the top, twelfth face was a linear assembly, a pair of arms three or four spans long, as densely packed with gears and linkages as anything from the age of clockwork.

Staying low, the occulter steered its way across the cabin until it was hovering in front of Agata’s feet; she could feel the spill of air against her skin. Then it ascended smoothly until it made contact with the calmstone slab – surrogate for the slopes of the Peerless itself. She gripped the slab tightly as four burred tips drilled obliquely into the stone. As Tarquinia had promised, the net force was purely vertical, so the weight of the slab bore most of it, and with the drills counter-rotating in matched pairs Agata felt no torque trying to twist the slab sideways.

After a few lapses the drills fell silent and the air jets cut off, leaving the device hanging.

‘Try to shake it loose,’ Tarquinia suggested. Ramiro ignored the invitation, but Agata slid her end gently from side to side, and when this had no effect she grew bolder and began rocking the slab back and forth. The linkage rattled alarmingly, but the four splayed drill bits remained lodged in place.

‘That’s reassuring, isn’t it?’ she said. ‘The mountain is hardly going to sway like that.’

Ramiro wasn’t so impressed. ‘It doesn’t tell us much about the real hazards. If there’s a hole under the surface, or a powderstone inclusion—’

‘If it comes loose that’s not the end of the world,’ Tarquinia stressed. ‘It can always fly back and reattach itself.’

Agata said, ‘Try the walking mode.’

Tarquinia tapped the remote. The four bits remained fixed in the stone, but the plate on which the drills were mounted began rotating on the end of its arm – or rather, the arm began rotating around the plate, swinging the entire occulter forward, carrying it from Agata’s end of the slab towards Ramiro’s.

When this repositioning was complete, the four drills at the end of the second arm pushed up against the stone and began biting into it. The new quartet managed to gain purchase with only the first set bracing them; there was no need to start up the air jets again. Then the first four went into reverse and disengaged from the stone, and the whole process began to repeat itself.

Agata watched anxiously as the machine whirred and clanked its way down the slope from her shoulder to Ramiro’s. If the slab was unrealistically smooth, at least they’d made sure that it wasn’t gravitationally level.