The Two Towers contains books three and four of The Lord of the Rings. It is different from the other two because the first book tells of the adventures and dangers that befall the majority of the Fellowship, and the fourth book tells of Frodo and Sam's journey to Mordor. The events in both books are simultaneous even though you read one and then the other.

Book Four

Warning!! If you do not want to know the story line and details of the books do not read the summaries. I highly recommend reading the books.