The hobbits run as fast as they can into the forest, finally stopping for a drink of water. They come upon a sort of rock wall and climb up natural stairs, where they meet an Ent, or Treebeard, as he calls himself. Treebeard is the oldest living creature in Middle-earth, a fourteen-foot guardian of Fangorn forest. He takes the hobbits to an Ent house and gives them drink and shelter. He knows Gandalf and asks the Hobbits for news of the outside world. When he comes to know about Saruman and how he has tamed orcs to serve him, he is angry. He decides to gather all the Ents and march to Isengard. Treebeard tells the hobbits that there aren't many Ents left because all the Entmaidens and Entwines have gone away and the Ents cannot find them. Due to no new Entings being born and the Ents growing old, the population is dwindling.
The next day Treebeard takes the hobbits to a meeting of Ents at Entmoot. Two dozen Ents are gathered and more come. The next day they march to Isengard. The Ents are angry at Saruman, their neighbor, who cuts down their trees and burns them without reason and who also trains Orcs not to be afraid of Fangorn. Pippin looks behind and sees the whole forest moving. The trees have awakened and are marching towards Nan Curunir, the valley of Saruman.
The Ents are a population on the verge of dying out. Their forces are weak and they have no force with which to repopulate. Still, they march toward death to fight Saruman, knowing that the greater good they can accomplish will live on as a legacy even if they do not.
The story now returns to the three travelers hunting for their lost companions. They find a leaf from Lorien and crumbs of food in the grass, as well as pieces of cut cord. They also find an orc knife. They follow the hobbit prints up to Treebeard's rock wall and when they climb up to the top they once more see the old man who had appeared earlier.
The old man comes to them and reveals himself to be Gandalf. He tells them that the old man they had seen earlier was not him but Saruman. He also tells them that their missing hobbit friends have gone with the Ents to Isengard, to fight Saruman. He tells Aragorn that he must go to their aid.
He tells them what happened when he fell into the abyss with Balrog. Gandalf held on to the enemy's heel and the Balrog took him up to the highest peak from where Gandalf flung the Balrog to its death. Gwaihir, who had been sent by Lady Galadriel, found Gandalf there. He was taken to Lothlorien, where he was clad in white and healed. Lady Galadriel's messages of caution are given to the three and they set off.
The White Rider (Gandalf) then summons Shadowfax, his horse, which he took from Theoden along with two others. Gandalf sets Gimli on his own horse and they ride off toward the halls of Theoden, Eomer's king.
Saruman becomes a more important villain than Sauron in this part of the novel. He has managed to pervert society by controlling the orcs and waging war on all his neighbors. It now becomes the mission of the others to stop him.
Now that Gandalf has returned from the dead, he serves as the captain of the hunters. He leads them to Theoden's halls, and tells the guards that they have come back to return the horses that Eomer had lent them.
The four companions enter the hall after leaving their weapons behind, but they do not get a warm welcome. Theoden is reluctant to show gratitude; he says this is because Gandalf almost always heralds bad news and asks for help. In truth, it is because Saruman has a secret hold on him in the form of his advisor, Wormtongue.
Gandalf frees Theoden from the wicked influence of Wormtongue. Gandalf then asks Theoden to release Eomer, who has been held prisoner of Wormtongue's counsel. Eomer returns and lays his sword at Theoden's feet. Theoden realizes his mistake in trusting Wormtongue. He decides that he will himself lead the riders of Rohan against Saruman. Wormtongue is sent away.
Theoden gives Shadowfax to Gandalf. He proclaims that Eomer his heir and Eowyn his sister are to rule in his place until he returns.
The war on the orcs escalates as the narrative remains diverted from Frodo, as well as Merry and Pippin.