Warning!This is a summary of the Book The Two Towers. It does not contain every little single detail about the book/movie. If you have not read the book there are some spoilers! If you have only seen the movie, then I suggest reading the book, there is a lot left out of the movie that is crucial in the book and some parts included in this summary are in the book and not the movie. Also, if you have not read The Hobbit, I suggest you do, that would help you understand the trilogy more.

Our story continues with Pippin & Merry being taken back to Orthanc, Sauruman's Tower by the Urukai, Strider, Legolas, and Gimli chasing after them, and Frodo & Sam trying to make their way through Mordor.
Frodo and Sam keep going in circles trying to get to Mt. Doom. One night while sleeping, Gollum attacks. Sam and Frodo subdue Gollum and he says he will lead them to Mordor.
Meanwhile, the last of the Fellowship are chasing after Merry & Pippin. They track them all the way to Rohan, the kingdom of Horsemen. One night while trying to get some sleep, Strider thinks he sees Sauruman dressed like an old beggar. In the morning, the three come across a Rohirrim, the cavalry of Rohan. They have seen & killed the Urukai, but have not seen Merry & Pippin...
Being very resourceful Hobbits, Merry & Pippin have managed to escape into Fangorn Forest. There they meet Treebeard, an Ent who was sent by Gandalf to help them. Together, they witness a meeting of the Ents, which takes at least three days.(It is much shorter in the movie.) While the Ents are talking Merry & Pippin are taken to Treebeards house where they drink the water that makes them taller.
Meanwhile, Strider, Legolas, and Gimli find out that the two Hobbits are still alive. They to travel into Fangorn to find the Hobbits. on their way they meet Gandalf the white, who is not dead. Together the four travel to the capital of Rohan to speak with King Theoden. The king has been imprisoned under Sauruman, but Gandalf breaks the spell. This is where Eowyn is first introduced. Theoden wants no more war and decided to move all of his people to Helm's Deep, a place no enemy has ever enetered. Eomer, the nephew of the king was banished, along with his men, whom Gandalf sets off to find.
Back at Orthanc, Sauruman builds an army of 10,000 Urukai to go and tear down the walls of Helm's Deep.
Here is where the movie differs from the book. There were no elves at Helm's Deep except for Legolas. But we can live with that. Anyway, The Urukai attack the battle ensues and the urukai get over the wall. Not by using explosives! We can forgive that too, for it was a well done scene. In short, Gandald arrives with Eomer & his men and the drive the Urukai into the forest that appears out of nowhere. Those are actually Ents who are truning into trees.
Back at the Ent "council". Merry & Pippin & the Ents decide it is time to teach Sauruman a lesson. The Ents are going to war! They march on Orthanc without much trouble(as Sauruman's army is at Helm's Deep being smacked down). The Ents take the tower & Sauruman is defeated.
Let's not forget out two unlikely Heroes and their not so trustworthy guide. Gollum leads them into Gondor, the Kingdom of men. Here is where Sam sees his first Ogliphant. They also run into Faramir. In the movie Faramir is a lot meaner than in the book. That's the one thing I didn't like about the movies, but I can't say anything else bad so I'll live with it :). Anyway, Frodo & Sam tell them all they can about why they are here & where they need to go. They also tell Faramir of what became of Boromir. Faramir in the end lets them go & gives them some rations.