You are in luck! Enotes has a chapter by chapter summary of The Scarlet Pimpernel.
To find the chapter summaries, you go to the page for the book. You can find it by searching in the search bar at the top of the screen. On the top of the screen (under the name of the book) you will see four blue tabs: Study Guide, Lesson Plans, Q&A, and Discussion. When you choose the Study Guide tab you will see a list of chapter summaries. All you have to do is click on the chapter.
As the story opens, French soldiers have had their numbers increased at the gates of the Paris because the number of French aristocrats who have made successful escapes has dramatically increased in the past several weeks. (enotes chapter 1 summary)
When you are getting confused by a book, you should try reading the chapter summaries and then reading the chapter. Then you will already know basically what is going on when you read the chapter. It will make more sense to you. You can also look back at the summary as you read, so that you can clarify confusing details.