" Nightweed. Barely mentioned because it is illegal in the Empire, even for Masks. It was outlawed a century ago, after it was used to assassinate an Emperor. Always deadly, though in higher doses, it kills swiftly. In lower doses, the only symptoms are severe seizures. Three to six months of seizures, I remember. Then death. There is no cure. No antidote. Finally, I understand why the Commandant let us escape from Serra, why she didn’t bother slitting my throat. She didn’t have to. Because she’d already killed me. "

― Sabaa Tahir , A Torch Against the Night (An Ember in the Ashes, #2)