Across the Shattered Isles, the Velpa Trading Company controls a brutal colony of prisoners, indentured servants, and laborers whose debts can pass to their children. When a cave-in traps five Yore and Gander miners underground, they follow the foreman Mortis through a forbidden section of the mine. There they discover sealed barrels, guarded workers, and entire deposits of black glints from which all light appears to have been drained. Bruce secretly takes one before the group abandons a mortally wounded Mortis and attempts to escape across an underground aquifer. Dolph dies fighting for a skiff, while a tentacled creature drags Bruce and others beneath the water. Bruce throws the black glint to the surviving skiff before he disappears. Clot and Randy reach the far shaft, but Yore and Gander guards strike Randy down and attempt to detain the survivors. Clot runs into the caldera with the black glint, leaving both miners' fates uncertain.

Elsewhere in the colony, Piccolo and a second group of laborers load a Yore and Gander galleon beneath the watch of Chowder. Black-clad freedom fighters attack with firebombs, killing Chowder and burning the ship as Teddy joins their cause and other workers scatter. Piccolo survives the investigation and is eventually granted passage away from the Shattered Isles. In the fishing town of Birkenstock, residents celebrate the Festival of Drowning by surrendering possessions, regrets, and hopes to Eth, believing the ritual protects them from the Tangled One's song. Flick steals offerings from the water and becomes entranced by a voice calling from the sea. Randall swims after him, but drowned women drag both men into the depths. Their bodies return within minutes, bloated and decayed as though they had been dead for days, while the town's Velpa mayor orders the celebration to continue.

After workers become sick near the black-glint shipment, the Velpa Trading Company bypasses Yore and Gander and covertly sends the barrels toward Gavra for study. The infected agent Aizen leads Brimley, Borgak, Ginny, El, and Ferb toward the port, concealing his worsening illness and the voices coming from the cargo. When the Sarexian Eclipse extinguishes Lunaris and the light across Tyve, Rue simultaneously touches the Veyan door within Ephthalas and accepts his chosen companions while the barrels explode, the black glints disappear, and faceless creatures of living shadow attack the caravan. Ferb invokes the unfamiliar god Azuron, whose golden light drives the creatures back, but most of the company is killed before moonlight returns. Ginny rejoins the survivors as they place the wounded Ferb upon a wagon and begin walking toward the port through the brightest parts of the road. When a passing shadow pulls El's beheaded body out of sight, the creatures are named at last: the Lightless.