Nesta and Cassian travel to the Prison to retrieve the Harp after Nesta's scrying revealed its location. Rhysand has armed Nesta with the sword she Made, and as they climb the mountain, Cassian reminds her of the rules for surviving inside: stay together, say nothing that might provoke the inmates, and leave with the Harp before it can be used against them. Entering the Prison deepens Nesta's dread, especially when Cassian silently indicates that Blue Annis is behind one door and then freezes before another marked cell that he identifies as Lanthys's.

Nesta finds the hidden passage from her vision and leads Cassian through solid rock into a secret chamber beneath the Prison. There they discover the Harp at the center of an ancient, warded room marked with star-like symbols and an eight-pointed star. Because Nesta believes the Harp may recognize her as the Mask did, she insists on entering alone despite Cassian's fear for her safety. The wards allow her through, and Cassian remains at the threshold while Nesta approaches the instrument.

When Nesta touches the Harp, it floods her with a violent memory of Fae trapped behind sealed stone, suggesting the instrument was once used to imprison enemies and even their children. The contact then throws Nesta into a vision of Queen Briallyn seated on a throne and wearing the Crown. Briallyn recognizes that Nesta has the Harp, threatens Gwyn and Emerie through knowledge gathered by her spies, and realizes where Nesta is. The mental connection ends when Nesta slams back into the chamber floor, pinned by the Harp's power while Cassian, blocked by the wards, can only call to her from across the room.

Unable to free herself, Nesta speaks directly with the Harp, which answers in a proud, sentient voice and calls her "sister." Nesta demands release, and the Harp tells her to pluck the first string. When she does, the pressure vanishes, implying the Harp can open doors and alter bindings through its strings. Nesta rises, takes the Harp, and returns to Cassian, explaining that Briallyn saw her through the Crown and that they must leave at once. Cassian's relief is immediate and intimate, and once they are safely out of the warded chamber, Nesta tells him she has named her Made sword Ataraxia.

As they walk back through the Prison, the closeness between them deepens. Nesta kisses Cassian and admits that Gwyn and Emerie are her friends and that she thinks Cassian might be her friend too; Cassian answers that he has always been her friend. But the tenderness is cut short when they return to the main passage. Cassian suddenly senses danger, shoves Nesta behind him, and orders her to run. The source of his terror is immediately clear: Lanthys's cell door stands open.