Myranda is a servant of House Bolton of the Dreadfort, her father being the castle's kennelmaster. She is one of Ramsay Snow's bedwarmers and his secret lover, whom Ramsay intended to marry, prior to his unexpected legitimization.
Myranda and Violet enter the torture cellar in which Theon Greyjoy is kept hostage, release the former Prince of Winterfell and put him on a bed. Then they attempt to seduce him, claiming they have heard the heir to Pyke is "well endowed". Violet claims Myranda was in training to become a septa but her sexual urges kept her from taking the vows. Theon is initially distrustful but cannot help but grow aroused when Myranda, stripped of her clothes by Violet, straddles him.
Suddenly, the girls are interrupted by a horn sounded by Ramsay Snow, who approaches his two servants and taunts Theon, telling him he too has heard about Theon's manhood, he then shows him a gelding knife. Myranda and Violet then watch as Theon is knocked down by Ramsay and held by two men while Ramsay proceeds to castrate him.
Some time later, Myranda joins Ramsay in hunting another bedwarmer, Tansy, whom she is jealous of, through a forest near the Dreadfort. She enjoys seeing the terrified girl being chased by her master's hounds for a while, but eventually shoots her through the leg with an arrow, and moments later watches her being mauled to death by the dogs.
Myranda later engages in sex with Ramsay as Yara Greyjoy and a group of ironborn climb over the walls of the Dreadfort to assault the castle.
Myranda accompanies the rest of House Bolton to their new home, Winterfell. She is present when the Boltons and their household gather at the castle's main yard to greet the newly arrived Sansa Stark and Petyr Baelish. She watches with obvious jealousy and anger as Ramsay greets his new betrothed, Sansa.
While in Ramsay's bedroom, Myranda discusses Ramsay’s upcoming marriage to Sansa, admitting her jealousy of her, especially since Ramsay had promised to marry Myranda back when he was a bastard. Ramsay disregards Myranda's insecurities, causing Myranda to proclaim that perhaps she will marry too and leave him. This angers Ramsay who violently tells her that she is his and she is not going anywhere, unless she continues to bore him with her petty jealousy. He threateningly reminds her what he does to people who bore him, and hearing this Myranda swears never to bore him again. He forces himself on her and she bites his lip before they have sex.
Later, as Sansa wanders around the castle, Myranda approaches her beside the tower where Jaime Lannister once pushed Bran Stark from the window. Myranda puts on a friendly façade, talking to Sansa about her mother’s demise and offering her condolences, which Sansa accepts, though she clearly sees through her. To help Sansa "remember" how things used to be before her family's untimely death, Myranda leads Sansa down to the kennels to reunite her with Theon.
The night of the wedding, Myranda is sent by Ramsay to draw Sansa's bath, an order neither woman is enthusiastic about. As she wrings the black dye out of Sansa's hair, Myranda advises her not to let Ramsay get bored of her, and tells her the fates of Violet, Tansy, and many other women. Sansa boldly asks if Myranda ever really believed that Ramsay would marry her, which stops the girl dead in her tracks. Sansa coolly declares that she is a Stark and Winterfell is her home: she refuses to be scared and nothing Myranda says will intimidate her. Silently fuming but unable to retaliate, Myranda asks if she is still needed. Sansa dismisses her. She is later present at Ramsay and Sansa's wedding, again looking on with jealousy as they are married.
During the battle between the Bolton soldiers and the forces of Stannis Baratheon, Myranda takes Theon and corners Sansa with a bow and arrow before she can escape under the orders of Ramsay to bring her to her bed chamber. After Sansa makes it clear that she is unafraid of death, Myranda admits that Ramsay needs Sansa alive in order to birth a heir to the North, though she still threatens to maim her with her arrow. Before she can release it, Theon grabs her, making her fire and miss. In the ensuing struggle, Theon throws Myranda off the rampart to her death, exacting revenge against the woman who played a role in his castration.
Ramsay Bolton's lover, Myranda was a willing companion in all his tortures and sadistic games, and threatened Sansa Stark after her arrival at Winterfell. Theon Greyjoy killed her when he and Sansa escaped Winterfell. Ramsay mourned her briefly then fed her body to his hounds.