The mystery revolves around the abbey library, situated in a fortified tower called the Aedificium. This structure has three floors - the ground floor contains the kitchen and refectory, the first floor the scriptorium and the top floor is occupied by the library. The two lower floors are open to all, while only the librarian may enter the last. A catalogue of books is kept in the scriptorium, where manuscripts are read and copied. A monk who wishes to read a book would send a request to the librarian, who, if he thought the request justified, would bring it to the scriptorium. Finally, the library is in the form of a labyrinth, whose secret only the librarian and the assistant librarian know.
The Aedificium has four towers at the four cardinal points, and the top floor of each has seven rooms on the outside, surrounding a central room. There are another eight rooms on the outer walls, and sixteen rooms in the centre of the maze. Thus, the library has a total of fifty-six rooms. Each room has a scroll containing a verse from the Book of Revelation. The first letter of the verse is the letter corresponding to that room. The letters of adjacent rooms, read together, give the name of a region (e.g. Hibernia in the West tower), and those rooms contain books from that region. The geographical regions are:
- Fons Adae, 'The earthly paradise' contains Bibles and commentaries, East Tower
- Acaia, Greece, Northeast
- Iudaia, Judea, East
- Aegyptus, Egypt, Southeast
- Leones, 'South' contains books from Africa, South Tower
- Yspania, Spain, Sothwest outer
- Roma, Italy, Southwest inner
- Hibernia, Ireland, West Tower
- Gallia, France, Northwest
- Germania, Germany, North
- Anglia, England, North Tower
Two rooms have no lettering - the easternmost room, which has an altar, and the central room on the South Tower, the 'finis Africae' (tip of Africa) which contains the most heavily guarded books, and can only be entered through a secret door. The entrance to the library is in the central room of the East Tower, which is connected to the scriptorium by a staircase.