At the northern edge of the habitable world there is a tear in reality — a vertical crack, ground to sky, through which you can see a version of the landscape that is almost right. Trees that spiral. Mountains that drift. A sky with too many moons.
The Ulvkin have guarded it for seven thousand years. Sentinel rotations last three months because longer breaks people. The breach cannot be closed — only held.
For most of recorded history, the Mouth was stable. In the last decade it has widened — three inches. That number sounds small until you ask the question the Veilwalkers ask: widened why? Nothing on their side of the watch has changed.
Something, somewhere, is stressing the seal.