The Sentinel tries to prevent anyone to approach the Singing Sisters. He lives in the shack outside their domain. There, travelers are greeted by him, an old man with a carved walking stick, the white stubble around the sides of his head is his only hair. To see the Sisters, visitors must convince the sentinel that they have a valid purpose. He is actually the sentinel as payment from a deal he made with the sisters a long time ago.
- Keys to the Demon Prison (Fablehaven #5)