Complex sentence: Though never verified, there is a strong indication that, Book was at one time an Alliance Operative, after giving Mal specific advice regarding the Operative that was attempting to assassinate River Tam: noting how they "move".
Split into simpler sentences: Though never verified, there is a strong indication that Book was at one time an Alliance Operative. After giving Mal specific advice regarding the Operative that was attempting to assassinate River Tam, noting how how Operatives "move".