For six hundred years, Marrowfen was surveyed after every fire, flood, and rebuilding. The city did not merely appear on the map. Roads, property lines, gates, and even household doorsteps became real because the accepted record said they were there.
Last winter, Deputy Clerk Ilyan Venn redrew the north line after a chimney spark. In the small hours, his ink skipped a quarter. No alarm sounded. The district simply stopped appearing in official editions—and, over the following weeks, stopped appearing everywhere.
The missing quarter now travels. Its folded roads, boundary stones, paper wings, and half-remembered houses follow old bearings toward the Datum Stone. Surveyors call them the Unpinned. They do not hate the city. They are only trying to return to it.
You are the final night surveyor. Your five instrument families were designed to amend mistakes, not wage war. Place them along the traverse, keep twenty seals in the datum, and survive until the clerk accepts a corrected edition at sunrise.
At the end of every survey, one sentence is entered in the margin: Leave room for the city.