‘No, this is perfect.’ Agata wasn’t sure how much explanation her early starts required. ‘I just have trouble planning the journey sometimes; if I’m not as energetic it can take me a few more lapses to get here, but if there’s any doubt I’d rather make sure I won’t be late.’

‘Hmm.’ Celia didn’t care. ‘Any new thoughts about the disruption?’

‘I’m still optimistic,’ Agata replied cautiously.

‘You’ve seen the ancestors’ writing,’ Celia acknowledged. ‘Of course that makes you hopeful. But they didn’t tell you how many of us survive.’

‘But nor did they mention a great tragedy,’ Agata replied. ‘They just offered their thanks. If the mountain had been shattered, you’d think they would have aimed for a higher level of solemnity.’

Celia was amused. ‘Six generations on? It will all be ancient history by then. They’ll carve their memorial on Esilio and some politician will make an empty speech.’ She handed Agata her tool belt and access key. ‘No one will know what our lives were really like, and no one will care.’

Agata said, ‘Perhaps.’

Agata forced herself to complete a full sweep of the tunnel, burning off every visible speck of moss. But as she raced back towards the site of her real work, when she noticed one faint red smudge that she’d missed she did not stop to pull her coherer from her belt.

She paused to disassemble the centre of the first grille, then she slipped through and continued down the tunnel. Her fellow worker who came here on an earlier shift had left a few mossy smudges of her own; no one was perfect. Agata reached the second grille with almost a bell to spare. She reached into her gut and pulled out her tools. The package was tied by a string to her first canister of disruptor.

Working on the grille in utter blackness was pure instinct for her now; her fingers gauged the narrow trench left by her previous assault and guided the drill to the right location with no intervening thought. Between bars, she only stopped to check the clock on her belt.

When she’d eased the fifth bar out and laid it on the floor of the tunnel beside her, she hesitated. Maybe there were invisible defences around the outlet – vibration sensors and high-powered coherers. Before the bombing that would have been unlikely, but anything was possible now.

Agata reached through the grille and sent one of the bars skidding towards the outlet. No weapon’s flash broke the darkness. She only had a few chimes left in her shift, and four days before her most optimistic deadline for starting the diffusion. If there ever was a time to take courage and tell herself she was untouchable, wrapped in the arms of the ancestors, this was it. She crawled through the broken grille.