Long ago, Zyltrix and the Siphon Order seal the Dios Ostium after taking a fragment of pure light from Tyve's interior. Zyltrix judges the other expeditionaries unworthy, entrusts the light to Horatio, and leaves the entire group trapped within Tyve. The abandoned members attack Horatio for the prize, forcing him to flee toward the archipelagos. In the present, the Harbingers escape the illusion surrounding the Shining Star and pass through its portal to the Twilight Temple. The Arbiter contacts Torrin long enough to warn that the enemy has not been stopped, that Torrin must recover the scepter, and that the scepter is a trap. The group then opens two dark chambers within the temple. One holds a mad scholar's research into Traeus, a legendary civilization lost beneath the sea. The other contains an empty sarcophagus dedicated to the Shadow of Light, where Torrin remembers Valence Avarith sealing away every remnant of Sethis.

On the chief's path, Bjorn shelters from the cold and awakens beside Skjold the Anvil and Magna Neva. They reveal that the summit's judgment was meant to expose what Bjorn truly sought. The scattered barbarians do not need another chief, but they may need a guide capable of carrying Skjold forward as a shared symbol. Skjold tells Bjorn that a chain forged through iron will can still break before a stronger spirit, while Magna Neva warns that another power has also taken an interest in him. At the Twilight Temple, Ernan awakens Whisper and asks him to abandon the Harbingers, take the portal network east, and escape Tyve together. Whisper refuses to surrender the larger purpose he has found, but assures Ernan that they remain brothers. Ernan's apology unlocks a memory that had been hidden from Whisper since the party first reached Piln.

In the restored memory, Piln's Arcanium reveals that the fragment of the Ithelion within the lighthouse is weakening. Martha proposes that the Harbingers steal it and carry it toward the Dios Ostium, while the Arcanium sacrifices every living person in Piln to reignite the lighthouse with extracted mortal light. The group refuses to act without a better plan. Ernan then recites the creed of the Chain, paralyzes the Harbingers, steals two Crystallic fragments, drains Helena's light, takes the light of Piln, and replaces their memories of the betrayal. In the present, Whisper attacks Ernan as the truth returns. The others attempt to restrain him, but his recitation binds nearly everyone in the temple. Ernan begs Whisper to flee with him, then accepts that the Harbingers have become his brother's true family. Declaring that only death can break the Chain, Ernan turns its fire upon himself and burns to death, releasing the others from its hold.