‘Let’s not talk about the details,’ Giacomo suggested. He’d had three years to think through the strategy; why would he be interested in debating it with someone who’d had three pauses?

‘All right.’ Ramiro clung to the guide rope in what he guessed was someone else’s living room. If the group had gone to so much trouble to bring him here, what did that imply about the end point of their discussions? But he had to stop thinking that way, or his decisions would all be shaped by the presumption that it was impossible for anyone armed with foresight to waste their time.

‘The occulters weren’t designed to carry anything,’ he began.

Giacomo tipped his head, acknowledging the fact without making an unseemly boast that he’d been aware of this before the occulters had even existed. ‘We put suitable hooks on the caches,’ he explained. ‘Spring-loaded to secure them. All your machines will need to do is visit the right locations along the way to the base, and the cargo will more or less attach itself. Our devices have been stuck in place with resin, but a lateral tug will loosen the bond with far less force than it would take to break it vertically.’

‘So you’ve managed to build a dozen of these things and smuggle them outside?’

‘A dozen and a half,’ Giacomo corrected him. ‘Including spares. In the end it was just a matter of stealth and patience. Everything was based on pre-existing designs; it’s only the delivery mechanism that would have been beyond us.’

Ramiro said, ‘Tell me about the bombs.’

‘They’ll do the job,’ Giacomo promised him.

‘I don’t doubt that. But what’s the size of each charge? The blast radius?’

‘In vacuum, they’ll fracture clearstone within six strides of the detonation point.’

‘That’s all?’

‘That’s enough,’ Giacomo insisted. ‘Once the light collector’s damaged, the channel will be dead.’

‘And do you know how well protected the internal light path is?’

Giacomo said, ‘There are three clearstone seals below the collector: at four strides deep, eight strides, and one stretch. Once you go past those three seals, the main tube itself is continuous – they don’t put anything between the mirrors, because that would cut into the light with every bounce. But there’s no chance of us breaching the tubes: the first seal alone will take most of the energy out of the blast.’

‘You’re certain of that?’ Ramiro wished Agata hadn’t given up on the plan before she’d heard these details.

‘That’s what the explosives experts tell me,’ Giacomo replied carefully. ‘Running a test on a mock-up would have been the best way to answer that, but there’s a limit to what we can slip past surveillance.’