Marcus is injured defending his fort against marauding Celtic forces.

Marcus is a young Roman centurion who has command of a fort on the British frontier in the first century A.D.  Rome, seeking to extend its empire, is not much loved in Isca Dumnoniorum; it is "a new slip grafted on to an old stock - and the graft had not yet taken" (Chapter 2).  The troops at the fort are taken by surprise, and they are grossly outnumbered as attackers "(swarm) in from every side...waves of shadows...pouring in to the attack...as if all Tartarus had broken loose".  After the first wave, the Romans send for reinforcements, but while they are waiting, they are attacked again and again.  In the last battle, the Celts arrive with chariots, with "whirling scythe-blades on the war-hubs of the wheels".  The Romans are powerless in the face of such might, and in a ferocious confrontation, Marcus is "flung down under the trampling hooves, under the scythe-bladed wheels and the collapsing welter of the overset chariot" (Chapter 3).  Although he survives, his thigh-bone is smashed, and the muscles around it "torn to shreds" (Chapter 4).