tldnr:
Ana and Christian take a helicopter to Seattle and Ana sees Christians sex dungeon for the first time.
Warnings: Besides the fact that this chapter ends with Ana stepping into a sex dungeon, it's actually pretty bland.
50 Shades is kind of like the novel-version of that time you had to stretch a term paper out from five pages to ten, so you adjusted the margins, added an extra space between each sentence, and then basically just typed in extra filler. Chapter 4 was a contrived excuse to get CG and Ana back in the same place at the same time; they wanted to be in the same place at the same time, only they had contrived reasons for not doing so, which resulted in a need for a second contrived reason to overcome the first contrivance so that the novel could move along again.
Chapter 5 is a bunch of foot-shuffling and throat-clearing, and in the end, CG is all, "Okay, I'll tell you my weird secrets, but I have to do it in Seattle." Chapter 6 is mostly waiting around for them to get to Seattle. Chapter 7 is all weird secrets, and Chapters 8 and 9 are just sex. Astoundingly inefficient! And, I expect, part of why you'll hear so many people talk about how they read the whole thing in a night. These readers may express genuine enthusiasm for the book, and state that they read it so fast because they enjoyed it so much. But, on some level, I expect plenty of people are reading this book quickly because there are just so many long stretches in which nothing of any importance is happening. Those stretches are quite easy to skim.
Like basically all of Chapter 6, for example!
(Editor's note: we did not skim. You know--for science!)