This book is the second installment of the Left Behind Series, written by authors Tim Lahaye and Jerry B. Jenkins.
Tribulation Force picks up where the first book, Left Behind, left off. The characters are the same- they follow Rayford Steele, Buck Williams, Chloe Steele (Rayford's daughter) and Bruce Barnes, a pastor who was not taken during the vanishing of believers in the first book. The plot line follows the actions of these main characters as they decide what their next steps will be as they try and rebuild their lives after the disappearances of millions around the world.
This book is obviously based of the Bible's Revelations chapter, as is the entire series. While the characters in the first book appear to be completely lost and bewildered in their faith, this book begins to bring them new understanding about God, and faith. The group of main characters form the "Tribulation Force" during this book; basically, they ban together to spread the word of God. They come to the realization that there will be seven years until God returns to the earth, and so they prepare themselves for the unsettled years to come.
I absolutely loved this book! The characters are all REAL; they are people that I could easily meet in my own neighborhood. The book is not preachy, but offers a lot of information and insight into Christianity that I believe would be very helpful for any interested reader. Perhaps more importantly, the flow of the book is great- it is a fairly easy read, and I must say it is hard to put down when you start it, so consider yourself warned. While you could probably pick this book up and read it alone, I would really suggest reading Left Behind first to understand the background story of the Tribulation Force.