[Aiwendil]

Tolkien has spent almost all of book I (with the exception of chapters 1, 6, 7, and 8) building up the suspense surrounding the Black Riders. It is in this chapter that the suspense really pays off, and gives us a climax to the first book that is both exciting and fulfilling.

Frodo's journey in this chapter seems almost to be a miniature version of his journey in Mordor. Here it is the Morgul blade that threatens to turn him into a wraith; later it is the Ring. In both cases he becomes increasingly weak and distant, so that the real business of journeying is handled by his companions. But in both cases he is in the end separated from his companions and forced to handle things by himself. And that's where the important difference comes - in this chapter he succeeds; he has his moment of heroism where he stands up to the Black Riders.

The climax here is, as Davem has already pointed out, far better than what Jackson and his team came up with. It completely undermines the scene for Frodo to have a companion at the end. In the book, there is sort of a miniature eucatastrophe. It appears not only unlikely that Frodo will escape; it appears hopeless. He is alone across the ford from the Nazgul. He cannot outrun them and he knows no reason that they should not be able to simply cross the river and reach him. He is saved by something totally unexpected - the power of Elrond over the river. It's not a huge climax, but it fits Tolkien's usual climactic structure perfectly.