When the centurion Lucius Cornelius Macro arrives on the shores of Britain to take part in The Emperor Claudius's invasion in the summer of A.D. 43, he knows he will be facing one of the toughest campaigns of his long, battle-scarred career. But nothing could have prepared him for the ferocious brutality and tenacious bravery of the British warriors. In a series of bloody battles, under the eagle of the Second Legion, Macro and his young subordinate, Optio Cato, and the desperately outnumbered Roman army, must find and defeat the enemy before they can grow strong enough to overwhelm the legions.

But the Britons are not the only foe facing Macro and Cato. A sinister organization opposed to the Emperor is secretly betraying the brave men of the legions. And when rumors of an assassination attempt coincide with the Emperor's arrival on British soil, the soldiers realize they are up against a force more ruthless than their acknowledged enemy, and that time is running out if they are to prevent Claudius's glorious victory from turning into disaster.