Nancy Drew is in Arizona. She's been invited to spend a short vacation at Shadow Ranch which is outside Phoenix. She soon discovers that it's having problems. A phantom horse has been seen racing through the nearby meadows, and there's been malicious damage to the buildings and fences. Could it all relate to a treasure hidden somewhere on the ranch by that 19th century outlaw, Dirk Valentine?

Librarian's note: the characters, settings, description, and other details have been done for the first five of the 1980s/1990s editions: #1, The Secret of the Old Clock, #2, The Hidden Staircase, #3, The Bungalow Mystery, #4, The Mystery of Lilac Inn, and #5. The Secret of Shadow Ranch. Librarian needed for #6 and on!