"The promise I had made to the demon weighed upon my mind, like Dante's iron cowl on the heads of the hellish hypocrites"

 

   A reference to Canto XXIII of Dante Alighieri's Inferno.  The heavy cowls which weigh down 'hypocrites' confined to the Eighth Circle of Hell are in fact described as comprising an outer skin of gold over a thick layer of lead.

Online edition of Dante Alighieri's 'Divine Comedy' as translated by Rev. HF Cary, M.A., (1805)