Duncan Carter, a seasoned Scottish guide, is drawn from the margins of history into a far more perilous legend when his old friend Miles Hollister arrives in Africa with a bloodstained journal and a desperate plea: find his missing brother Charles, last seen in the forbidden Mongala Territory. Duncan leads him toward a place whispered about in fear-an enslaved village, a volcanic mountain, and a power no European map has ever named.

There, beneath the shadow of the volcano, Duncan, Miles, and Charles discover that the true masters of the mine are not merely men but the enigmatic Pledans-pale, otherworldly beings armed with impossible devices, ruling through fear and pain. Captured and forced into brutal labour, the three must unravel their secrets. As every escape attempt exacts a terrible cost, they are locked in a struggle for freedom.