The Return of the King (Book Three, Lord of the Rings Trilogy)

The Battle for Middle-Earth has begun . . . almost. First, Gandalf and Pippin must journey to the grand city of Minas Tirith, capital of Gondor, a realm of men. They must warn the Steward of Gondor, Denethor, that Sauron's army has left Mordor and is now approaching the city. However, still bitter after his son Boromir's death, Denethor commands Pippin to become a tower guard to pay his debt for 'what he did'. As his other son is nearly slain defending  the surrounding lands, and a force of some 200,000 Orcs gather around the city, slowly Denethor descends into madness. When the full forces of darkness finally converge, with the Ringwraiths (also known as Nazgul), the lieutenants of Sauron, in the lead, all seems lost. However, Aragorn, rightful ruler of Gondor, has a plan. There were once a nation of men that pledged allegiance to Isildur, the First King of Men. When he called on them for battle they refused and were cursed to spend an eternity waiting for their rightful ruler to call on them once more. Aragorn hopes to enlist these men in battle against Sauron and the Orcs. If he fails, the world falls. Meanwhile, in Mordor, Frodo has been taken prisoner by the Orcs and is being held in the tower of Crith Ungol. Sam rescues him, but Frodo, weak after his imprisonment, is unable to carry the One Ring of Sauron. So, in his stead, Sam loyally carries the Ring. As the seconds creep by, they come closer and closer to Mt. Doom, the one place where the ring can be destroyed. However, every second they waste is another second that Sauron gains power and another second that the Ring slowly corrupts their souls. Will they reach Mordor in time and blot evil from the land at last, or will the darkness overwhelm all good and all that it stands for?

The Return of the King is the final installment in the Lord of the Rings epic. The prequel to the prequel, The Silmarillion, was published after Tolkien's death. So the order, chronologically at least, is The Hobbit, The Lord of the Rings, and The Silmarillion.