Aragorn, Legolas and Gimli follow the orcs to rescue Merry and Pippin. They are stopped by the Riders of Rohan. Unknown to everyone, Merry and Pippin escaped when the Riders attacked the Orcs.
They went into the Forest of Fangorn and met Treebeard, an Ent who hates Orcs because they killed his trees. He gets the other Ents to attack Isengard, Saruman's home.
Gandalf comes back to life and meets Aragorn and the others. They ride to Edoras, capital of Rohan. Gandalf persuades King Theoden to fight against Saruman. The Orcs attack the fortress of Helm's Deep, but are beaten.
The Ents destroy most of Isengard, where Gandalf and the others meet up with Merry and Pippin. Gandalf and Pippin, magically seen by Sauron, set off for Gondor. Aragorn reveals himself to Sauron as the King of Men, who decides to attack.