Dan said ‘Oh shit’ very softly, and Jeff watched with numb despair as he hurled himself down the steps of the neighbouring pit.

It was clear from the way one of Lucy’s legs was bent under her, as she lay on the floor of the second pit, that she was badly hurt. Dan grabbed her up in a fireman’s lift and rapidly made his ay back to safety. And, even though Jeff could see nothing but the chamber ceiling through Dan’s A/V, he felt an appalling certainty the second pit was already filling with the same deadly black oil.

And then, just as Dan reached the top, the lights went out.

They followed the rampart to where it merged into a tunnel leading deep inside Vault One. They moved on past branching corridors and ramps to either side, each leading up or down to other levels and chambers. The beams projected from their suits flashed reflections off hastily epoxied signs printed with luminescent inks, which were mounted near junctions that had not yet been fully explored. All carried explicit warnings never to leave the already lit paths.

Catching sight of these warnings, Jeff found himself thinking once more about Rodriguez.

David Rodriguez had been an engineer recruited to the ASI’s retrieval-and-research branch several years before to help run the remote reconnaissance probes, but instead had quickly become the stuff of legend for all the wrong reasons. He was the one recruits got told about during their training and orientation, as an example of how not to conduct oneself when exploring the Founder Network.

He had been part of a standard reconnaissance into a then unexplored level of Vault Two, and had ignored the warnings about sticking to the approved paths. Instead, he had wandered into a side chamber, trying to find a probe that had failed to report back.

He had found the probe and, some hours later, his team-mates found him.

Time, it turned out, worked differently in the side chambers of that particular level. It became slower, the farther inside them you got. Rodriguez had discovered this when he stepped up next to the probe, probably thinking it had simply broken down.

He was still there, to this day: right foot raised and looking towards the far wall, his face turned away from the chamber entrance as he headed forward, still clearly oblivious to his fate. That alone was what really sent the shivers down people’s spines; the fact that no one could see his face got their imaginations working overtime.