The story picks up with Gandalf and Pippen arriving in Gondor. They tell Denethor of the death of Boromir, and Pippen pledges his his services to Denethor in memory of Boromir becoming a guard of the city of Gondor. They had only been in Gondor a few days when Sauron begins his attack on the "Dawnless day" and Faramir is sorely hurt. The battle has begun and things look bleak for Gondor. They are so bleak indeed that Denethor, the steward, has lost hope and prepares to burn himself and his wounded son, Faramir. Pippen intervenes and later, with Gandalf's help saves Faramir, but Denethor commits suicide.
Meanwhile in Rohan, the invaders are put down and the soldiers of Rohan are regrouping to march to Gondor. Aragon is visited by relatives who tell him he should take the Path of the Dead. Aragon leaves to follow their advice with only Legolas and Gimli as companions. Merry is distraught to be left behind but a Eowyn, the niece of Thoeden, promises to take him secretely to Gondor.
In Gondor the battle continues to be fought and Sauron's forces push forward. just when it looks as if the city will fall, the Riders of Rohan attack. In the ensuing battle, Theoden is killed, and Merry and Eowyn manage to kill the Witchking, the leader of the Nazgul. They are gravely wounded in the process. Aragon finally saves the day with the armies of the Dead who have followed him to fulfill an age old oath. For the moment, anyway, Gondor is reprieved.
The remaining leaders in Gondor decide to put together an army to take to the Gates of Morder. They have no illusions that they can win a battle, but they are trying to direct the Eye of Sauron at themselves so that, if possible, Frodo can complete his Quest to destroy the Ring.
Now Tolkein turns his attention to Frodo and Sam. Sam sneaks into Morder, finds, and frees Frodo. They then begin to make their way to Mount Doom. It is a harrowing trip. They have little food or water, and the Ring is preying on Frodo's mind causing him great distress. The strategy of Aragon in bringing an army to the gates of Morder pays off for Frodo and Sam as nearly all the Orcs begin heading for the gate, clearing the path to Mount Doom. Frodo and Sam barely make it to the top. Sam has to carry Frodo the last part of the way. When they get there, Frodo finds he cannot part with the Ring and claims it as his own. At that moment Gollum attacks Frodo from the darkness cutting off Frodo's finger claiming the Ring for himself. The momentum of the attack carries him too close to the edge and he falls into Mount Doom destroying the Ring. Morder begins to crumble and Frodo and Sam lay down to die. They are rescued at the last moment by the Eagles.
When they awaken it is to a new age of Men. They are heroes and Aragon is king. Eventually the Hobbits begin to make their way home and they find that all evil is not gone from the world. The defeated Saruman had escaped and went to make trouble in the Shire. Sam, Merry, and Pippen become heroes as they free the Shire from his evil grasp. Then all four settle down to life in the Shire. That life is good for Merry, Pippen, and Sam, but Frodo cannot overcome the mental and physical injuries he sustained as the Ring Bearer. In the end, he joins Gandalf and Elrond and departs over the Sea.