Like the Characters essay, this will attempt to chronicle a number of alterations made by PJ to the plot of The Lord of the Rings that had a major effect either directly on the plot or to themes of the book. Also like the Characters essay, this list is not exhaustive.
The Hornburg, part 1: the bloated battle
In The Two Towers the film, the Battle of Helm’s Deep is the climax according to PJ himself (in a manner similar to the film Zulu). On the other hand, Tolkien saw the Battle of the Hornburg (Helm’s Deep being a ravine, not a fortress) as follows:
“If both the Ents and the Hornburg cannot be treated at sufficient length to make sense, then one should go. It should be the Hornburg, which is incidental to the main story; and there would be this additional gain that we are going to have a big battle (of which as much should be made as possible), but battles tend to be too similar: the big one would gain by having no competitor.” (Letter 210, my bold emphasis)
The lack of importance of the Hornburg is evident when one considers what each event accomplishes for the plot. The Hornburg results in the elimination of Saruman’s army and gives Aragorn a chance to be a leader. The Ents and Isengard result in the destruction of Saruman’s fortress and remaining forces, the capture of Saruman himself, and the capture of the Palantir (which has a huge effect on the war with Sauron himself). PJ, evidently preferring battles over more significant events, expanded the battle to take up a significant portion of the film with the build-up beginning even before the Three Hunters reach Edoras. On the other hand the Ents are reduced to just a few scenes of (sometimes comic) relief from the tension of battle.
The Hornburg, part 2: the Elves
One of the major themes of Tolkien’s book is that the Dominion of Men is soon at hand, and that the era of the Elves (especially the High Elves) is nearing its end. As such they defend their homes in Mirkwood and Lorien and only destroy Dol Guldur after Sauron has been defeated, but do not play a major role in the War of the Ring. This theme is briefly mentioned in the film of The Two Towers when Galadriel states that “the time of the Elves is over”, but this line is promptly followed by “do we leave Middle-earth to its fate?”
The second line shows that the filmmakers completely missed the point of the first: the Elves do not have the strength left to make a major effort to save Middle-earth, especially since two of their realms are in close proximity to Dol Guldur. In the films, however, an army of Elves from Lorien (who bear messages from Elrond for an unexplained reason) march to aid in the defense of the Hornburg. Leaving aside the obvious issues such as the ludicrous speed with which they traveled and the uncertain source of their knowledge of where the Rohirrim were taking refuge, this clearly flies in the face of the theme of fading.
A common response to this by revisionists is that PJ had to, or at least wanted to show the audience that the Elves were fighting in the War of the Ring since PJ couldn’t show the battles of the Elves. However, this misses a major point: The Lord of the Rings is not about Elves. The Silmarillion is, but that happens thousands of years prior. Expanding the role of the Elves, even to show the audience that they were not inactive, goes directly against the book on multiple levels.
In a stark departure from the book, even by the films’ standards, Frodo tells Sam to leave him and “go home” in The Return of the King. This is one of the more blatantly obvious changes to the story, reflecting both the weakening of Frodo to corruption by Gollum and the weakening of the theme of friendship found in the book. According to screenwriter Philippa Boyens in the EE documentary features for the third film the filmmakers wanted Gollum to get “payoff”, for Frodo to be shown as not “angelic”, and for Frodo to enter Shelob’s tunnel alone so that it would be more “dramatic”. In no way were these changes necessary for adaptation to film, they merely represent (by the filmmakers’ own admission) their personal preferences.
The Army of the Dead
The primary change to the Dead Men of Dunharrow, aside from their color, is their martial role. This is reflected in the very name used to refer to them: Tolkien never mentioned the “Army of the Dead”. In the book the Dead drove the Corsairs from their ships in fright, but their actual ability to fight is left ambiguous since the only weapon they needed was fear. Aragorn released them after they drive the Corsairs away; a wise move since if he had brought them to Minas Tirith his allies would also have fled the field.
In the movie however the Army of the Dead is brought all the way to Minas Tirith and completely annihilates the enemy. This raises two issues. First, it is uncertain why Aragorn doesn’t have them stick around for a few more days and take on Mordor itself since he already brought them that far. Second, it renders the sacrifices made on the field of battle (particularly Theoden) seem rather worthless. Far from the battle taking many hours and many more deaths to win even after Aragorn’s arrival the Army of the Dead surges across the Pelennor and wipes out the enemy in a matter of minutes. If only Theoden had taken a few hours longer to show up he would have survived and the battle would still have been won by the Dead.
The Scouring of the Shire
This, along with the omission of Tom Bombadil, is probably one of the most discussed cuts from the story. However, it is significant: the Scouring was the climax of the hobbits’ journey in the story. After saving Middle-earth by destroying Sauron they return to their own home, traditionally safe from evil, to find that it too has been corrupted while they were gone. They are then able to, on their own, rally the Shire-hobbits and defeat those who had taken over their home. This earns them the respect of their fellows rather than the reputation for oddness that Bilbo had. The Scouring is thus the culmination of the Hobbits’ journey towards maturity and independence that began when they started to realizejust how dangerous the wider world was during their journey through the Old Forest.
On the other hand PJ thought it so obvious that the Scouring should be cut that he called the decision a “no-brainer”. The filmmakers’ point out that the climax of their films is the destruction of the Ring and that they cannot go on for too long after that, but it misses the point. Tolkien himself described The Lord of the Rings as “primarily a study of the ennoblement (or sanctification) of the humble” (i.e., hobbits) in Letter 181 and the Scouring specifically as “an essential part of the plot, foreseen from the outset” in the Foreword to the Second Edition of The Lord of the Rings.
While the destruction of the Ring is – of course – very important, the Scouring is the true end of the War of the Ring and of the story. It is only anti-climactic (as some have suggested) if one has an oversimplified concept of the climax of The Lord of the Rings.
The plot, like the characters of the story suffered many undue changes at the hands of the filmmakers. While no one can reasonably deny the necessity of condensing and making minor alterations to the story when adapting it. These examples represent major changes to the story itself, which rather defeats the point of adapting an existing story instead of creating an original one.