Sky Silvestry was a businesswoman and a passenger aboard a tourist craft on the planet Midnight.
Sky was visiting Midnight after departing from her wife. When an unknown force began banging on the side of the vessel, Sky panicked, imagining the entity had come for her alone. Specifically, she said, "She said she'd get me." The force, apparently feeding on her fear, possessed her.
When first possessed, Sky repeated everything that everybody said. Then she said the same thing at exactly the same time. Jethro ended up concluding that Sky was no longer in control of her own body. The passengers were terrified by this and decided they wanted Sky thrown off the bus to her death, to which the Tenth Doctor objected. Sky began to repeat only the Doctor's words and then shortly after, she spoke them before him and left him repeating her. The other passengers believed the life-form had left Sky and had now possessed the Doctor, but in reality, the entity had stolen the Doctor's voice.
Sky convinced the others to throw the Doctor off the bus. The hostess realised Sky was still possessed because she used the phrases "Allons-y!" and "Molto bene", which only the Doctor had used earlier. The hostess grabbed Sky and pulled her out the door, sacrificing herself to save the Doctor and the other passengers on board the shuttle. (TV: Midnight)