The map with a gap
David D. Connell and Jim Thurman
Mathnet detectives Kate Monday and George Frankly use math skills like triangulation and scale to find a buried treasure in a ghost town.

by Brad Strickland and Thomas E. Fuller (1999)
When they help restore the Skeleton Reef Lighthouse for the Oakland Historical Society, Joe and Wishbone discover that the lighthouse holds the key to incredible treasure and to some dark and dangerous secrets.
David D. Connell and Jim Thurman
Mathnet detectives Kate Monday and George Frankly use math skills like triangulation and scale to find a buried treasure in a ghost town.
Betsy Byars
At the eerie Hunt mansion, Herculeah Jones has been reading aloud to Lionus Hunt, an elderly stroke victim who can only communicate by blinking his eyes (once for yes, twice for no). Mr. Hunt seems to be trying to tell Herculeah something, but his gruff nurse won't allow her to ask any questions. What is Mr. Hunt trying to say? Is it related to a murder that took place in the mansion's black tower years ago? And who is the creepy old lady who lives in the mansion? Herculeah's friend Meat thinks she may be asking for trouble, but Herculeah Jones won't quit until she gets to the bottom of this mystery.
Josh Lacey
Tom goes with his Uncle Harvey to Peru, where they narrowly escape imprisonment and death as they hunt for buried treasure after tracking down a journal written by John Drake, a young relative of Sir Francis Drake, on a voyage to Lima in 1577. Includes biographical information on John and Francis Drake.
M. G. Leonard
Darkus Cuttle has taken care of his father ever since his mother died, but one day his father vanished from a locked vault at the Natural History Museum, and now he lives with his eccentric uncle--but one day he finds a large and unusually intelligent and self-aware beetle, and soon he and his two friends are caught up in a struggle to protect an intelligent super species of beetles.