Finn and Lily struggle to assemble the final Wishing Tree Ornaments because the prevailing town resonance is causing materials to repel their intended anchor points, making adhesives fail and fragile structures crumble. Finn realizes they need a counter-force rather than just glue, recalling historical mentions of structural stabilizers. Cora, an apprentice usually relegated to sorting rejected items, arrives with a small sack of dark green stones labeled 'Grotto Seal Samples.' These stones, historically used near the river for early winter displays, emit an intense, inert coldness. When placed inside the ornaments, the Grotto Seal stones successfully lock the silver foil stars and stabilize the spun-sugar garlands, providing a non-adhesive anchor against the resonant push. However, their supply of the Grotto Seal is critically low, forcing Finn and Lily to realize they must search the entire inventory of rejected items for more of this vital, cold counter-agent before the main Solstice lighting ceremony.