Jack the kelpie surfaces them onto Insmoor's shore, half-drowned. Hyacinthe is briefly knocked unconscious. Oak leaves the others to recover and scouts the rocky island, where he finds Wren alone on a boulder, looking anguished. Using his honey-mouthed charm, he lures her close, intending to kill her, but as he draws his blade he reconsiders the puzzle of her behavior—her warnings, her unexplained silences, her cryptic mention of her sister Bex. He realizes Bogdana is blackmailing Wren by holding Bex hostage, forcing Wren into vows that prevent her from telling the truth.

Wren confirms his guess with her relief and gives Oak the white walnut containing Tiernan, warning that if he can't help her, she may become his enemy. Oak rejoins Hyacinthe and Jack and deduces Bex is being held by Mother Marrow in Mandrake Market.

Oak confronts Mother Marrow, who refuses to surrender Bex. He wagers a year and a day of servitude against three guesses for Bex's location. He correctly identifies the cabinet of nuts but Mother Marrow demands he pick the exact one; when he begins destroying them, she traps him inside an acorn with Bex herself.

Inside the acorn, Oak meets Bex, who has been warned about him and distrusts him. He explains Wren is being coerced and that he intends to help. Hyacinthe and Jack break in from outside, freeing them from the acorn. Oak dismisses Mother Marrow's debt in exchange for her silence.

Bogdana arrives, having sensed her plan unraveling. Oak orders Jack and Hyacinthe to take Bex to Wren while he holds off the storm hag. After a brief clash, Oak offers to surrender if Bogdana takes him directly to Wren. She agrees, intending to make him her prize in the sister's place.