The Two Towers Book 3, Chapter 9
The others remain behind with Merry and Pippin. They want to know many things about their journey. They go into a guardhouse to eat some food. Aragorn asks to hear more about ents but Pippin says that he will have to wait and actually see one. The hobbits had found pipe tobacco from their homeland in one of the storerooms. They each take out their pipes and lie back to relax. After a few moments of silence, the hobbits begin the story of their nine-day ordeal. Aragorn gives Pippin his cloak and brooch back and presents them with the weapons he found that they dropped at Boromir's side.
They explain the conflict between Grishnakh and Ugluk. Then they tell of the rallying of the ents and their march towards Isengard with hundreds of trees following. Most of Saruman's army was marching away when they arrived. The ents stood still and sent a band of trees called the Huorns to follow the army. The ents attacked the fortress and were pelted with arrows. Saruman did not understand his attackers. They let men go and destroyed the walls. He fled into Orthanc. Treebeard told them to watch over the tower while he and the ents diverted the Isen river into the city to clean away the blood and put out the fires of Saruman's furnaces. At dusk, Gandalf appeared and demanded to see the old ent. Treebeard was happy to see him, "'I am glad you have come...wood, water and stone I can master, but three is a wizard to manage here.'" Book 3, Chapter 9, pg. 223. Gandalf spoke to the hobbits a little and then left with more trees to attack the orcs besieging Helm's Deep.
Through the night, the hobbits watched the ents dam up the Isen and then flood Isengard. Since the waters flooded, Saruman has been watching them dissipate around Orthanc. In the morning, Grima appeared and announced that he was a messenger from Theoded who wanted to speak to Saruman. Treebeard was told to expect him by Gandalf and he told him to either wait for Gandalf or flee inside to his master. He went inside and Treebeard set the hobbits before the door. Aragorn is surprised that there is tobacco from the hobbits' land in Isengard. Ents gathered food from storerooms to feed Theoded and his men. They wonder where Gandalf is and Aragorn decides to peruse the ruins of Isengard.