The Lord of The Rings: Return of The King (book 3) by J.R.R. Tolkien

The armies of the Dark Lord Sauron are massing as his evil shadow spreads even wider. Men, Dwarves, Elves and Ents unite forces to do battle against the Dark. Meanwhile, Frodo and Sam struggle further into Mordor, guided by the treacherous creature Gollum, in their heroic quest to destroy the One Ring