When Amy and Dan Cahill's quest to find the million dollars takes them to Japan, they must decide whether or not to enter into an alliance with their uncle, Alastair Oh, whose motives for helping them are extremely questionable.

As Cruz and his friends continue to search for the third piece of the cipher, a mysterious message arrives suggesting that someone close to him is working for Nebula, leaving Cruz unsure of who he can trust.

"Amid assignments that take the Explorer Academy recruits from the iceberg-filled waters of Antarctica to the bone-dry deserts of Argentina, Cruz Coronado is scrambling to complete the last piece of the cipher. With Nebula agents and the elusive explorer spy still out there, his opportunity to recover his mother's world-changing formula is slipping away. But as Cruz has learned from his time aboard Orion, true explorers must never give up. Even after...