The Plot Twist at Mount Doom

Chapter 3 of The Return of the King contains one of the book's greatest plot twists, Frodo's inability to destroy the Ring.  All throughout The Lord of the Rings, so much discussion pertained to the Ring's destruction that by the time Frodo and Sam reached Mount Doom, we too as the readers felt as though we had traveled all the way with them.  Over 900 pages of plot led to this moment, and it felt as though the weight would be lifted off our shoulders right with Frodo as he cast the Ring into the fire.  Except, he did not.  Right in the midst of the story's climax, Frodo pulled back the source of his suffering and succumbed to its temptation.

I personally cannot remember my initial reaction when I first read this scene, but even now I am impressed that Tolkien took something that was destined to be predictable, the Ring's destruction, and turned into something unforgettable.  He does this with firm evidence backing up Frodo's decision.  All along the way, we see the hobbit grow weaker and weaker as he carries the burden of the Ring and especially after his startling accusation against Sam in the tower of Cirith Ungol.  The reader suspects something is not alright with Frodo, but the Quest must go on.  

Tolkien also carried out this plot twist without sacrificing his happy ending.  It would have been easy for Tolkien to have made the Quest an ultimate failure.  Frodo cannot destroy the Ring.  Gollum takes it back at the edge of the Cracks of Doom, and rather than falling into the fire, he could have walked out, and all hope would have been lost.  The forces of good would have been defeated, and the whole story would have ended tragically.  I do not perceive this plotline ever being part of Tolkien's plan.  No, the happy ending was absolute.  The Ring would be destroyed, just not in the way the reader suspected it to be.

Tolkien once again proves his prowess for storytelling.  By taking something predictable and changing it enough to be familiar yet unforeseen, he could both shock and satisfy his audience.  That's quite an effective plot twist.