Vision

Cause two can keep a secret if one of them is dead.

Luna sighed. "Do you mind untying me?"
Pris got to work on her hands. "It's rope. It's rotting. How did it get in here?"
Luna shrugged. "Theo likes me. He tried to kiss me."
Pris snorted. "What? Did he do it?"
"Yes!" said Luna. "It's not funny!"
Pris pulled off the rope. "Whatever. Your call. Anyway, what are you going to do about him?" She gestured to the puddle of blood, and the person collapsed in it.
Luna stood up and shook herself off. "I'm not sure. He's a good person at heart."
"Theo means god."
"I mentioned that on the first day I was here, Pris. Remember?"
Pris nodded. "It picked up on the wires." She blinked. "My eyes hurt. I should go back to bed."
Luna bit her lip, and pulled Pris to her feet. "You do that. Get rest and heal."
Pris touched her eye. The pupil was a slit of clouded gray, and the iris was sky blue with violet streaks. "Someday."
The girl had been born blind in one eye, and she had slowly been deprived of vision in the other eye as she grew, until finally she was completely sightless. When One had discovered her, she had given her sight, but she had never come back completely. Everything was blurry and she was colorblind. She could only see one color- purple. This was the reason she only wore violet clothes. She spent most of her time in her room, monitoring the Palace through wires and cameras.
"Ew," said Luna. "Don't touch your eye,"
"It doesn't hurt," sighed Pris. "What's the point. Anyway, I'm leaving. Good luck with Theo," She said as she stepped out of the room. "Bye."