They’d almost come full circle back to the apartment, but Agata couldn’t face the piles of unread books again. She wasn’t going to transform herself into Medoro in the next few bells. ‘We had a time-reversed camera on the Surveyor for years,’ she lamented. ‘I could have spent all my free time experimenting on it, if I’d known how useful that would be.’

Serena was amused. ‘The rest of the crew might not have been too happy if you’d destroyed it.’

‘After we’d left Esilio it wouldn’t have mattered. But we certainly took care of it until then.’ Agata stopped and stood clutching the guide rope, thinking about the landing. ‘Protecting it from too much exposure.’

‘You mean not pointing it at Esilio’s sun?’ Serena frowned. ‘Though wouldn’t that have . . . brought it back to normal, if it had arrived burnt out?’

‘Protecting it from too much ordinary light as well,’ Agata said. ‘Intense light would have damaged it: scatter from our engines, say.’

‘So you want to steal the Surveyor and aim its engines at the base of the mountain?’ Serena joked.

Agata said, ‘No. But a big enough explosion above the base should have the same effect . . . or twelve smaller ones might do it.’

Serena understood. ‘You want to repurpose the saboteurs’ bombs? Use the flash but not the bang?’

‘Why not? The collectors gather light from all directions – and they can’t discriminate between ordinary light and time-reversed light. If we can shift the explosions far enough away from the surface that there’s no risk of them breaching the tubes, they could still be the cause of the disruption. They don’t even need to damage the cameras permanently – they just have to overwhelm the photonics long enough for the time-reversed light that’s in transit to be lost.’ The original plan for the occulters had been to blind each channel to a single star, but the design that made that impossible rendered this new plan far less demanding: it didn’t matter where in the sky the explosions appeared. The collectors would funnel all the photons in and dazzle the cameras, regardless.

Serena said, ‘What if there’s a sensor that can bring down a shutter if the ambient light gets too bright? I mean, the light that’s meant to do this damage will be bouncing back and forth between the mirrors before it gets to the camera. There’ll be plenty of time for news of the danger to reach the camera by a shorter route.’

She was right, Agata realised. But it might not matter. ‘They can bring down a shutter to protect the camera from permanent damage . . . but that shutter will block the time-reversed light, too. So it will all come down to the timing: whether the flash from the explosions forces the shutter to close for so long that the signal is lost.’