Pendragon: Journal of an Adventure through Time and Space

1. 

   The Quillan Games (Pendragon #7)

   D. J. MacHale

2. 

   The Soldiers of Halla (Pendragon #10)

   D. J. MacHale, William Dufris

3. 

   The Rivers of Zadaa (Pendragon #6)

   D. J. MacHale

4. 

   Raven Rise (Pendragon #9)

   D. J. MacHale

Book data and covers from Open Library (openlibrary.org).