The Dead of Night by Peter Lerangis

This book finds Dan and Amy rescuing Atticus and heading off to Samarkand looking for a stale orb (i.e. an astrolabe). Frankly, this book is a lot more of the same--adventure, codes to be solved, blatant disregard for authority in favor of the family expertise. I'm interested to see what's going on with the kids' father--who has been alive all these years, and at the very least was a Vesper once. For such smart kids, it seemed to take them a long time to figure out the stale orb/astrolabe connection.