From the introduction:
Down in the gully lies a row of tombs, each home to a poor knight who perished fighting the pagans that opposed the Prophet. A low cave enters into a plain corridor, stairs leading down to a simple tomb with a stone slab, on which the remains of the knights lay. Four pillars, each depicting one of the saints, watch over the deceased and support the chamber’s ceiling.
None of these tombs hold anything of value; even the bones of the knights have long turned to dust.
All except one: this tomb seems as unremarkable as the rest, but a secret trapdoor beneath the stone slab leads to a series of secret tombs, the real resting place of the Prophet’s knights.