Harmony is a Red and was a member of the Son of Ares. She helps Dancer bring Darrow out of Lykos after he "dies." Darrow notes that Harmony is more aggressive and vengeful than Dancer. She gets Evey away from Mickey, knowing that Mickey is not a kind master. It is later revealed that she chose Titus to infiltrate The Institute the same way Dancer chose Darrow.
In Golden Son, she tells Darrow that Dancer is dead and that Ares wants him to sacrifice himself by carrying a bomb into a gala where many high ranking Golds will be. Harmony has been conducting terror bombings against the Golds, though many lowColors are harmed in the crossfire. Darrow is dissatisfied with her methods and her manipulations of Evey, who Harmony uses as a bomber. She manages to convince Darrow to lay the bomb at the gala when she reveals to him that Eo was pregnant when she died. However, Darrow does not go through with the attack, instead starting a civil war amongst the Golds. It is later that she betrayed Dancer and Ares as she was not satisfied with their more cautious and passive strategy.
She is captured by The Jackal, and informs him of the identity of Ares and Darrow's true heritage as a Red to get out of captivity, betraying her cause out of spite of Ares true identity.
Half of her face steam-burned.