The Drowned Lock

They drained the canal to mend it. By dawn the lock-keeper lay where the water had been.

Silas Reed was found at first light face down in the drained basin, his head broken against the lower gate. The canal had been emptied at dusk for the masons and would not be filled again till the work was done; the mud lay smooth and the channel held no water a hull could float. Five of the canal folk were awake along the cut that night. Each gave an account of the dark hours. One of them swears to a journey the empty channel could not have carried.

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You're given the cipher type. The key is yours to find.