Gallchobhar turns Vis's sacrifice into an act of deliberate cruelty. After stabbing Vis, Gallchobhar publicly beheads the surrendered king Rónán, shocking both the defenders of Caer Áras and many of his own men because the killing violates the respect due to a king. As fighting breaks out near the gate, Gallchobhar kicks the badly wounded Vis into Lake Áras to drown.

On the lakebed, Vis is unexpectedly met by his father. Vis's father frees Vis's bound arm, places his life-preserving medallion around Vis's neck, and uses it to keep Vis alive despite the stomach wound and the lack of air. When Vis tries to refuse the sacrifice, his father comforts him, shares a final embrace, tells him to have courage, and dies as the current carries him away. In the aftermath of that loss, Vis discovers that he can now feel and control his silver arm because he has somehow imbued it.

Realising the battle above has already begun, Vis walks back toward shore. He calls out Gallchobhar's name and rises from the water before both armies, understanding that his survival at dawn will look like a sign from the gods. When Vis picks up Lir's staff, he is pulled into a mental space where Lir, though physically dead, tells him to challenge Gallchobhar and proclaim that the gods rejected the sacrifice. Lir says that if Vis kills Gallchobhar, Fiachra's warriors will surrender, and he strengthens Vis before sending him back.

Back on the battlefield, Vis follows Lir's instructions exactly. He announces that Dia Domhain has anointed him a draoi nasceann, condemns Gallchobhar and Fiachra's followers for dishonouring the Old Ways, and orders the warriors to stop fighting. The battle stalls as both sides watch. Gallchobhar attacks in desperation, but Vis's silver arm blocks his blows without damage, even shattering Gallchobhar's sword when Vis catches it. Because Gallchobhar cannot break Vis and his own men refuse to rejoin the fight, Gallchobhar is forced into a duel he is already losing in spirit.

The fight continues until Gallchobhar's confidence collapses. Even though Gallchobhar inflicts several severe wounds, the medallion and Lir's aid keep Vis standing long enough to cripple him, disarm him, and answer Gallchobhar's insult by declaring that Gallchobhar was never truly worthy. Vis then kills Gallchobhar with his own spear through the heart and leaves the body displayed for all to see. With their champion dead and Vis seeming divinely protected, Fiachra's forces break, fleeing or surrendering, and Vis reaches the gates of Caer Áras before finally collapsing unconscious inside.