Cahills vs Vespers hard cover books 1,2,3 & 6

The 39 Clues is a series of adventure novels written by a collaboration of authors, including Rick Riordan, Gordon Korman, Peter Lerangis, Jude Watson, Patrick Carman, Linda Sue Park, Margaret Peterson Haddix, Roland Smith, David Baldacci, Jeff Hirsch, Natalie Standiford, C. Alexander London, Sarwat Chadda and Jenny Goebel. It consists of five series, The Clue Hunt, Cahills vs. Vespers, Unstoppable, Doublecross, and Superspecial. They chronicle the adventures of two siblings, Amy and Dan Cahill, who discover that their family has been, and still is, the most influential family in history