Rust was assigned to watch over Lief, Barda, and Jasmine when they were accepted into the troop by Bess. She gave them their masks and told them who each would be reporting to for training.
Outside of Happy Vale, Rust and Lief both witnessed the Masked One's phantom kill Fern when she looked through Lief's bags. Rust was relieved that it was just a "barefaced hanger on" that was killed, and not another of the inner circle.
Later, once Barda explained their desire to head north and leave the Masked Ones, Rust was overjoyed to see them go. However, her good mood was spoiled when Kree tricked Bess into drinking poison meant for Barda. Jasmine tried to help save Bess by removing her mask of adulthood, but it had bonded to her face and her actions only tore the skin off Bess' neck. When the rest of the troop saw this, they rebelled in disgust. Rust defended Bess' body along with the other members of the inner circle, and summoned the barrier moths to attack the defecting members of the troop. In the confusion she and the rest of the Masked Ones fled.
Barda chased after the Masked Ones in an attempt to regain the companion's supplies, but he was drugged and left on the side of the road. Rust later sold the supplies to Steven for some Queen Bee Honey.
Rust wore a fox mask that was permanently bonded to her skin.
Rust is very distrusting of strangers, and never for a moment thought the companions were not spies. She is fiercely loyal to the Masked Ones, though only those either young or accepted as full members of the troupe, as she treated older individuals accepted in by Bess with as much disdain as anyone else.
Rust was able to control the barrier moths with a high pitch shriek. It is possible she had performance abilities as well due to living with the Masked Ones, but what they are is unknown.