The Stone Organs were four stones bonded with the power of a goddess that were used to give four mortals the power of gods.
Long ago, four skilled Librarians divided the Nameless's Sister, with the assistance of the old Librarian known as Binder, and together they separated her power into four stone organs, each containing great magical power which could turn them into gods. The Stone Organs where then bound to the four skilled Librarians, one organ for each to have within their body. This gave them the powers of a God, and these four Gods are now known as Iris, Bacchus, Aengus and Heka. The Four new Gods feared the old Librarian known as the Binder, for only he knew how to turn them back into humans. Due to this, the four new gods cursed Binder into a book, and continued their immortal lives, hiding Binder away so no one could find him.
The Nameless and his Hunt
Once the Nameless had escaped from Castle Blackspire he, along with the main crew, began to hunt down the four gods who had the Stone Organs within them, so he could kill and extract such pieces to reform his sister. Firstly, the Nameless was sent to Fillory, where he sent Josh to secretly poison Bacchus, from which point Nameless conjured a knife which he used to open Bacchus's chest, and take the Stone Organ for himself. After that, the Second Stone organ was extracted by Iris after she revealed herself in a park to kill Julia and her friends for failing to catch Nameless, from which point he ripped the Stone organ out of her chest. The third Stone organ within Heka had been lost, as Heka died centuries before, however Julia came into possession of it somehow. The final Stone Organ was ripped out of Aengus's chest while he was attempting to flee to his hiding cave.