The protagonist, Humphrey, having lost his parents in a siege against his small village by Saracen pirates, nourishes an unquenchable hatred against these enemies. His uncle, a former engineer in the Byzantine army, takes care of the boy and teaches him the ancient art of building siege machines. Humphrey spends his adolescence studying at the school of an important cathedral, where a monk, a teacher of dialectics, discovers his skills as a mechanic, considering them useful for a work described secretly in an ancient Roman volume; thanks to that work it would be possible to establish an alliance and perpetual peace between the two shores of the Mediterranean, a project desired by the Duke of Apulia, Roger, son of the king of the same name. One summer, after a shipwreck, the protagonist is kidnapped by corsairs and, dragged in lootings and raids on the Greek coast, ends up eventually on Italian soil and returns home, escaping the massacre of a Byzantine captain. Eventually he will manage to become the king's greatest engineer, but far away and hidden.