The Library Devils are a group of devils that run a massive library of ancient and forbidden knowledge deep in one of the hellish planes. The library they work from is sealed from the inside, keeping the devils from physical contact of any kind; as a result, they must fill the shelves of their infernal space with knowledge given to them by communications through spells and incantations. As the true identities and histories of the individuals are unknown, they are generally referred to in tandem with one another. Their true motives remain unknown, but at the very least, they appear to thirst for any form of information not yet in their library.
The hero Wander was given a ritual spell (Infernal Library) by the arch-devil Etarus that allowed him to contact the library by writing to them in a blank book. As all communication done in this way was through writing, making it difficult to gauge the intentions of the devils. For any information they gave, they first required information of equivalent value. Wander gave them a detailed description of the Peas' dealings with Tarisi, as well as an account of their interactions with ley lines, including the location of a ley line under Hymathel and the effects that the energy had on the party. It is unknown what end this information provided them with.