You farm Level 61 of Greywell, a silo sealed deep underground. Every month the Council posts a bigger figure, and Steward Vance comes down the stair to collect it in potatoes.
The trouble is the seed. Greywell has replanted clones of the same potatoes for two hundred years, and each generation yields a little less. The Council’s ledger knows exactly how bad it is.
Then someone knocks on the door at the end of the west tunnel, from the other side. Behind it is a silo that survived without Greywell, and down the drain line lies Mire, one that didn’t. The founders owed Mire a debt they buried in the records. At the bottom of it all is a vault holding the last clean seed, and you decide who it belongs to.