The Three investigators mysteries

1. 

   Book 7

   The Mystery of the Fiery Eye

   Robert Arthur

2. 

   Book 15

   The Mystery of the Flaming Footprints

   Robert Arthur, M. V. Carey

3. The Mystery of the Invisible DogM. V. CareyCarey

   M

   Book 23

   The Mystery of the Invisible Dog

   M. V. Carey

4. 

   The Mystery of the Green Ghost

   Robert Arthur

5. The Secret of the Haunted MirrorM. V. CareyCarey

   S

   The Secret of the Haunted Mirror

   M. V. Carey

6. 

   The Mystery of Death Trap Mine

   M. V. Carey

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