The Two Towers continues Frodo's quest as begun in The Fellowship of the Ring. They've lost companions, and while Frodo and Sam continue towards Mount Doom, the rest of the Fellowship continues on their own journey down the River Anduin.
The Lord of the Rings maintains the breaks between the 3-volume set, as well as Tolkien's division of the text into six 'books;' page numbers follow the 'books' as if they were in one volume, not three; Volume II contains pages 401-725 pages, softcover.