Britain, 47 CE. Tribune Marcus Flavius Cursor, chief engineer of Legio XIV Gemina, arrives with the newly appointed Governor Scapula to find the province testing Roman resolve. After a brutal winter campaign to prove imperial authority, Cursor is dispatched into the unmapped western territories — Silures country beyond the Severn — to survey sites for permanent fortresses and exploit rich iron deposits in the ancient limestone hills. The locals warn against the deep places. Roman engineers do not take warnings from barbarians.
When the mines begin consuming men in ways no accident report can explain, Cursor finds himself caught between an empire that demands results and a threat that predates Rome itself. What emerges from those deep chambers has been sleeping for generations, kept dormant by knowledge the Celtic druids have preserved at terrible cost — knowledge the legions have now destroyed. With his command structure in denial, his soldiers dying, and Rome’s political machinery indifferent to causes it cannot categorise, Cursor must decide how far a Roman officer can reach beyond the boundaries of his world before he loses it entirely. The answer may require him to become the kind of man Rome has no record for.