The Abyssal Lexicon

In the oppressive, candlelit confines of a medieval scriptorium, a frail young scribe named Rowan falls under the mind-altering influence of a forbidden, abyssal text. His protective older sister, Elara, must risk her own sanity and descend into the monastery's flooded, subterranean archives to break the cosmic hold an ancient entity has on him before he is utterly consumed.