An archipelago known as Lantern Reach glows with living lanterns and magic that travels through light. A rare Lunar Convergence threatens to tear the veil between realms. The party is drawn to Lumenport, the lantern-lit capital, where a courier collapses in the alley clutching a parchment bearing a single glowing L. The note warns that the Lattice of Lost Letters has fractured and must be reassembled before the moon reaches full, or darkness will overrun the isles.

Main quest: retrieve four lattice fragments hidden in diverse locales and reweave the sigil:
- Brinehall Library beneath the drowned quay; solve waterlogged puzzles and outsmart wardens of salt and ink.
- Gloomwood, a sentient forest where whispers become testimony and guide to a hollow treant guarding a fragment.
- Volaris Ridge, a volcanic pass with magma puzzles and a fire kin guarding the fragment inside a lava shrine.
- Clockwork Docks, a district of moving cranes and lantern golems; repair a temporal trap to reveal the fragment.

Side quest: investigate a rogue postmaster who dispatches letters that plant visions and foretell deaths; uncover a traitor within the Lantern Keepers and secure a wary ally in the Guild of Light.

Central events: The Lunar Convergence demands the lattice be whole. The Umbra Archivist seeks to steal letters to rewrite history; without the lattice, rifts spill shadow beasts into the isles. When reassembled, the lattice can seal the rifts or, misaligned, unleash a worst nightmare.

Hooks: a glowing L sigil appears in dreams as a living map; a lantern festival with a misdirected bulb that heralds danger; a courier begging aid with a sealed letter that refuses to be opened.

Rewards: Luminant Blade +1 that sheds bright light; Lantern of Quietude to silence sound within 60 feet for 10 minutes once per long rest; Lattice Cloak grants advantage on stealth in dim light; Lapis Letters to cast Sending once per long rest.