The tenth battle was waged on the banks of a river which is called Tribruit.
Caius Hectorius Moderatus and Ualcos Magesos return from their mission to Londinium. Moderatus tells his father that Ælle has had their family’s villa sacked, and their family has been sent to some of his allies in Gaul — precisely where has been kept a secret. As word of this spreads among the other commanders, Lugh Striking-Hand, Quintus Badiovirus, and Peredur hatch a plan to capture Æthelflæd — who is following them, according to the Saxon raider they captured in the mountains on the way to Deva Victrix — and try to exchange her for Caius’s family, or at the very least assurance of their well-being. Caius resists the plan, believing that Ælle cannot be trusted to hold up his end of the deal, but Peredur, having already been ambushed by his own father once, goes out on his own, hoping to be captured. He is, and brought to the ruins of an old villa, where Æthelflæd throws him in a pit, and begins trying to turn him the same way she did his father. The other knights arrive to rescue him, and take Æthelflæd prisoner. She scoffs at their plan, saying that they do not understand a warrior’s spirit; her father is perfectly willing to sacrifice her.
Though captured, Æthelflæd’s plans still create a problem for Arthur and his army: she has gathered bandits and mercenaries from across the island to stop Arthur before he reaches Viroconium. Arthur sees this as an opportunity, though: victory would mean crushing a significant portion of the island’s lawless elements in one fell swoop, adding legitimacy to his claim to the High Kingship. On the eve of battle, Nennios approaches Arthur’s camp to speak with his old comrade, Caius Hectorius, and plead with him to turn away. He tells Caius that many of the old veterans have become mercenaries, and if Arthur’s army continues, he will have to face many of his old brothers-in-arms in battle, and none of them want that.
In the battle, Arthur’s army fends off the brigands, while Caius Hectorius charges into battle against the mercenaries. Vorcunos and his pack of werewolves dive into the ford, eager to kill Arthur’s warriors. Badiovirus unleashes his polybolos, then leaves his warband to prepare another volley while he personally rides up to the ford to duel Vorcunos alone. Vorcunos proves a powerful opponent, however. His werewolves bite and claw at Badiovirus, and Vorcunos breaks his ribs and hacks off his left hand with a hatchet, leaving the knight with his head bashed against a rock and presumed dead. Lugh beseeches the mercenaries to help them defeat Vorcunos, finally offering them an honorable way out of their contract with Ælle. The warriors spend the remainder of the gold from the hoards recovered around Eboracum to pay the mercenary bands to join their army.
Peredur notices that Badiovirus is actually still alive, so he is taken to Myrddin. Peredur asks Arthur for the right to execute his father personally, which he grants, but he wants to keep him alive until after the war, so that he can execute him in Londinium amidst the proceedings that will follow. When Badiovirus awakens in Myrddin’s tent, Myrddin challenges his foolish concepts of Roman virtus which led him to this condition, and promises an education to follow.