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 and showing him a gelding knife. Myranda and Violet then watch as Theon is knocked down by Ramsay and held by twomen while Ramsay proceeds to castrate him.
In the A Song of Ice and Fire novels, there's no mention of a Bolton servant named Myranda. The TV series often re-uses established given names from the books for minor characters, because these are names already known to exist within the fictional world of Westeros. In this case the TV character shares her name with Myranda Royce, a noblewoman of the Vale.
There are no women among Ramsay Snow's servants, known as "the Bastard's Boys", who assist him with his atrocities.