The knock

Then a sound. Faint at first—like something shifting behind the far wall. A second knock followed. Then another. The crew snapped to attention. Sarah raised a hand to silence them. More banging came, followed by muffled shouting. “Voices,” Jules said. “Somebody is alive in here!” The sound came from behind a large metal door near the far end of the room, half-covered in debris and broken pipework.
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