A succession of shutters sealed off portions of the final length of the cooling tunnel, opening in sequence to allow air to pass from chamber to chamber at ever lower pressures until it was expelled into the void. The maintenance hatch wasn’t meant to open unless the whole cycle had been stopped and all the chambers had reached the ambient pressure of the mountain’s interior, but Serena’s technician friends had managed to fake the sensor data to convince the hatch that it was safe to operate. The only catch was that it had been too complicated to try to lock it against any real part of the cycle. It would be up to each person exiting to synchronise their access with a time when the shutter below them wasn’t open to the void.

Agata pressed her helmet to the hatch and listened to the sequence of clanks and hisses until the rhythm was embedded in her mind. The last time she’d dealt with machinery in the tunnels it hadn’t ended well, but at least she’d had the timing right.

She slid the hatch open. Air blew in from behind her, but it only took a flicker for the pressure to equalise. She climbed into the tunnel and braced herself against the walls with her hands and feet. Serena closed the hatch behind her.

Agata waited in the dark, mentally composed but still viscerally terrified: there was absolutely nothing about the situation that her body found acceptable. She heard the creaking of the shutters above her and the sibilance of expanding gas drawing nearer.

A span from her head, the rotating disc of the shutter above her finally swung its aperture around to coincide with the tunnel. Agata felt the air rising up across her cooling bag, moving the opposite way to the usual cycle now that she’d wrecked the pressure gradient. But the sensors had been numbed – the anomaly would pass unnoticed.

When the shutter closed there was nothing to feel, and in the perfect darkness no way to be sure that it had happened. But then the exiting wind rustled the fabric on her limbs and starlight entered the tunnel from below. Agata didn’t look down for confirmation; she just brought her limbs together and let herself fall.

Half a dozen strides from the outlet she drew a circle on her chest and the jetpack eased her to a halt, supporting her as she followed the rotation of the Peerless. She sketched an upwards arrow and ascended, until a safety handle set into the rock for maintenance workers came within reach. Wide-field cameras on the slopes monitored the space around the mountain, with their feeds analysed automatically to detect anyone in trouble falling away into the void, but as long as the team remained close to the hull they’d be out of view.