The Two Towers is composed of Books 3 and 4, recounting the deeds of
the company after the breaking of the Fellowship of the Ring. The story
begins with the repentance and death of Boromir, who has tried
(unsuccessfully) to wrest the ring away from Frodo. Merry and Pippin
are kidnapped by orc-soldiers and they are taken towards Isengard,
while Aragorn, Legolas, and Gimli are in pursuit. The Riders of Rohan
appear, led by Éomer the Marshal, and they destroy the orcs. The
hobbits escape and meet Treebeard, the Ent, secret master of Fangorn.
Treebeard rouses the Tree-folk against Isengard and the forces of evil.
Meanwhile, Aragorn, Legolas and Gimli cross paths with Éomer and they meet Gandalf again, who is returned from death as the White Rider, veiled in grey. With Gandalf, they advance to the halls of King Théoden and Gandalf heals the king and rescues him from the spells of Wormtongue, an evil counselor who is in secret league with the enemy. The combined forces continue on towards Isengard, a fortress that has been destroyed by the Tree-folk. Saruman and Wormtongue are trapped in the tower of Orthanc. Saruman will not repent before Gandalf and so Gandalf breaks his staff and removes him from the council of wizards. Wormtongue throws a stone out of the window but he fails to it Gandalf; the stone turns out to be a palantír, one of the Seeing Stones of Númenor. Peregrin picks it up and gives it to Gandalf, but later in the night he falls to the lure of the palantír and steals it. When he looks into it, he is revealed to Sauron. Gandalf forgives Pippin and he gives the palantír to Aragorn, riding away (with Pippin) towards Minas Tirith.
Book Four (the second half of The Two Towers) focuses on Frodo and Samwise, who arelost and wandering through the somber war-torn region of hilly Emyn Muil. Gollum (who is also called Sméagol) as been spying on the hobbits and following their trail. Here in Emyn Muil, Frodo tames Gollum and Gollum serves Frodo (at least temporarily) as a servant serves his master. Gollum leads Frodo and Sam through the Dead Marshes until they reach the Morannon, the Black Gate of the Land of Mordor in the North. They are unable to pass through the gate and so Frodo accepts Gollum's advice to seek a "secret entrance" which is at the western walls of Mordor in the Mountains of Shadow. As they continued on the journey, the travelers encountered Faramir, the brother of Boromir, who was leading a scouting-force of the Men of Gondor. Faramir learns about the Ring but he overcomes the temptation that overcame his brother, Boromir. Faramir helps the hobbits by replenishing their dwindling supplies. Frodo, Sam and Gollum make their way to Cirith Ungol, the Spider's Pass. Faramir warned Frodo and Sam that this pass was a place of mortal peril, of which Gollum had told them less than he knew. The travelers reach the Cross-roads and take the road that leads to Minas Morgul; in the darkness, they can see the mobilization of Sauron's first army, led by the black King of the Ringwraiths.
Gollum guides the hobbits to a secret path that strays away from the city and they reach Cirith Ungol. Here, Gollum betrays the hobbits, intending to lead them to a monster called Shelob, who would devour them. Gollum's plan is frustrated by Sam's bravery: he chases Gollum away and wounds Shelob, as well. Frodo is stung by Shelob and he appears dead. Sam concludes that he must continue the quest alone and abandon his master, but as he is about to cross into Mordor, Sam overhears the orcs. He learns that Frodo is not dead but drugged. The orcs carry Frodo's body down a tunnel leading to the rear gate of the tower and Sam is unable to keep up with them. He passes out and Book 4 comes to an end.