Yuddha Kanda, the Book of War, opens with Rama's monkey army, joined by Ravana's own estranged brother Vibhishana, who defects rather than support his brother's injustice, building a great bridge of floating stones across the ocean strait to reach Lanka, a structure Hindu tradition identifies with the geological formation known today as Rama Setu or Adam's Bridge. The war that follows unfolds across many days of battle against Ravana's vast demon army, including devastating confrontations with Ravana's giant brother Kumbhakarna, woken from a long enchanted sleep to fight, and his son Indrajit, whose magical weapons repeatedly wound and nearly kill Lakshmana, requiring Hanuman to fly to the Himalayas and return carrying an entire mountain of healing herbs when he cannot identify the specific plant needed.
The climactic duel between Rama and Ravana ends with Ravana's death, after which Rama, rather than immediately welcoming Sita back, requires her to undergo agni pariksha, a trial by fire, to publicly demonstrate her chastity had remained unbroken during her captivity, a test she passes unharmed, protected by the fire god Agni himself, after which the reunited family returns to Ayodhya, where Rama is finally crowned king, inaugurating the celebrated era of just rule remembered as Rama Rajya.