With twenty days left in the Centennial and Terra near collapse, Isla refuses to accept that the search for Lightlark’s heart has failed. Three days after returning from Vinderland, Isla goes to Oro’s room and insists they begin again from the most basic truth: how Oro learned about the heart.

Oro says he read about the heart in an old book from a hidden library. The answer shocks Isla because Celeste had been right about such a library existing. Oro reveals the concealed room behind his balcony door, a large secret library filled with books and enchanted objects. Isla realizes the bondbreaker may be there, though Celeste’s poisoned state and Terra’s danger make the heart more urgent.

Before reading, Oro tells Isla something he had withheld because he expected Grim to explain it: Lightlark was created not only by Oro’s ancestor Horus Rey and Grim’s ancestor Cronan Malvere, but also by Isla’s ancestor, Lark Crown. Oro says the island was named after Lark and that this knowledge was lost over thousands of years. Isla understands that Oro needed her because only a Sunling, Wildling, or Nightshade can find and unlock the heart.

The revelation changes Isla’s understanding of the curses. If the heart can only be accessed by those three lines, then one of their realms may have used it to cast the curses. Isla considers whether a Wildling ancestor, Oro’s brother Egan, or Grim’s father could be responsible, though Isla still wants to believe Cleo must be involved.

After hours of research, Oro translates only limited information: the heart contains pure Sunling, Wildling, and Nightshade power, greater than modern ability, and remains hidden until it blooms and becomes part of Lightlark when most needed. Though they still do not know where it is, Isla feels the library is the key and persuades Oro to rest.

At dawn, Isla visits Celeste in the room where Grim hid her. Isla apologetically tells Celeste she was right about the hidden library, then notices Celeste’s hand clenched into a fist. Isla opens it and finds a clue Celeste must have seized before the poison immobilized her: the diamond ring Isla had given Azul.