The corridor had no name in the registry. It appeared on none of the maps Kai had been issued, though the survey team's environmental sensors confirmed it had existed for at least six years — longer than three of the four team members had held active classifications. Finn called it the spine, because it ran north-to-south beneath every other passage they had mapped, and because walking it felt vaguely like being swallowed by something that had not yet decided whether to digest you.
Kai was twelve steps behind the others when it happened.
Not a sound. Not a vision. Nothing as coherent as a hallucination. It was pressure — a sudden, complete, deliberate pressure behind his sternum, as though something had placed a hand flat against the inside of his chest and pushed. Not violently. Carefully. The way you would press a door to test whether it was locked, or to feel whether something warm was standing on the other side.
He stopped walking.
