Summary
Awakening from a dream of Gandalf fighting the Balrog in Moria, Frodo Baggins finds himself, along with Samwise Gamgee, lost in the Emyn Muil near Mordor. They discover that they are being tracked by Gollum, a former bearer of the One Ring. Capturing Gollum, Frodo takes pity and allows him to guide them into Mordor, despite Sam's reservations.
Aragorn, Legolas, and Gimli pursue a band of Uruk-hai to save their companions Merry and Pippin, entering the kingdom of Rohan. The Uruk-hai are ambushed by a group of Rohirrim, allowing Merry and Pippin to escape into Fangorn Forest. Meeting Aragorn's group, Rohirrim leader Éomer explains that he has been exiled with his men by Rohan's king, Théoden, who is under the control of Saruman and his servant Gríma Wormtongue. Éomer believes Merry and Pippin were killed during the raid but leaves the group with two horses. In Fangorn, Aragorn's group encounters Gandalf, who, after killing the Balrog at the cost of his own life, was resurrected as Gandalf the White to help save Middle-earth.
Gandalf leads the trio to Rohan's capital, Edoras, and frees Théoden from Saruman's control. Aragorn prevents Théoden from executing Wormtongue, who flees. Théoden evacuates the citizens to Helm's Deep as Saruman, who has knowledge of the fortress's only weakness, sends an army of Uruk-hai to destroy them. Gandalf seeks Éomer and his followers to support their king. Aragorn connects with Théoden's niece, Éowyn, who becomes infatuated with him. When Saruman's Warg-riding Orcs attack the refugees, Aragorn falls and is presumed dead, but he has visions of Arwen before being found by his horse, Brego. He rides to Helm's Deep, witnessing Saruman's army approaching the fortress.
In Rivendell, Arwen is told by her father, Elrond, that Aragorn will not return. He reminds her that if she remains in Middle-earth, she will outlive Aragorn by thousands of years, and she reluctantly departs for Valinor. Elrond is contacted by Galadriel of Lothlórien, who convinces him that the Elves should honor their alliance to men, and they dispatch a company of Elves to Helm's Deep.
In Fangorn, Merry and Pippin meet Treebeard, an Ent. Convincing Treebeard that they are allies, they are brought to an Ent council, where the Ents decide not to participate in the coming war. Pippin asks Treebeard to take them toward Isengard, where they witness the deforestation caused by Saruman's war effort. Enraged, Treebeard and the Ents storm Isengard, trapping Saruman in his tower.
Aragorn arrives at Helm's Deep, warning Théoden of Saruman's army. Théoden prepares for battle despite being outnumbered. A company of Lothlorien Elves arrives to aid Rohan just before the attack. The Uruk-hai breach the outer wall with explosives and kill the Elves' commander, Haldir, in the charge. The defenders retreat to the keep, where Aragorn convinces Théoden for a final charge. At dawn, Gandalf and Éomer arrive with the Rohirrim, turning the tide of battle. The surviving Uruk-hai flee into Fangorn Forest, where the Ents kill them. Gandalf warns Sauron will retaliate.
Gollum leads Frodo and Sam to the Black Gate but recommends they enter Mordor by another route. Frodo and Sam are captured by Rangers led by Faramir, younger brother of the late Boromir. Frodo helps Faramir catch Gollum to save him from being killed by the Rangers. Learning of the One Ring, Faramir takes his captives to Gondor to bring the Ring to his father, Denethor. As they pass through the besieged city of Osgiliath, Sam warns Faramir that Boromir was driven mad by the Ring's power. A Nazgûl nearly captures Frodo, but Sam saves him and reminds a disheartened Frodo that they are fighting for the good still left in Middle-earth. Impressed by Frodo's resolve, Faramir releases them. Feeling betrayed by his capture, Gollum decides he will reclaim the Ring by leading Frodo and Sam to "her" upon arriving at Cirith Ungol.
Source: Wikipedia (CC BY-SA 3.0)